Association of oxytocin augmentation and duration of labour with postpartum haemorrhage: A cohort study of nulliparous women.

OBJECTIVE: Both duration of labour and use of oxytocin for augmentation are known risk factors for postpartum haemorrhage but distinguishing between the significance of these factors is complex. In this study, we aimed to investigate the association between both labour duration and oxytocin augmentation, for postpartum haemorrhage. DESIGN: A cohort study based on a secondary analysis of a cluster-randomised trial. PARTICIPANTS AND SETTING: Term nulliparous women with a single foetus in cephalic presentation, spontaneous onset of active labour and a vaginal birth. The participants were originally included in cluster-randomised trial conducted in Norway from December 1, 2014, to January 31, 2017, that aimed to compare the frequency of intrapartum caesarean sections when adhering to the WHO partograph versus Zhang's guideline. MEASUREMENTS: The data were analysed through four statistical models. Model 1 investigated the effect of oxytocin augmentation as a dichotomous variable (yes/no); Model 2 investigated the effect of the duration of oxytocin augmentation; Model 3 investigated the effect of the maximum dose of oxytocin; and Model 4 investigated the effect of both the duration of augmentation and the maximum dose of oxytocin. All four models included duration of labour divided into five time-intervals. We used binary logistic regression to estimate the odds ratios of postpartum haemorrhage, defined as blood loss of ≥ 1000 ml, including a random intercept for hospital and mutually adjusting for oxytocin augmentation and labour duration in addition to maternal age, maternal marital status, maternal higher education level, maternal smoking habits in the first trimester, maternal body mass index and birth weight. FINDINGS: Model 1 found a significant association between the use of oxytocin and postpartum haemorrhage. In Model 2, oxytocin augmentation of ≥ 4.5 h was associated with postpartum haemorrhage. In Model 3, we found an association between a maximum dose of oxytocin of ≥ 20 mU/min and postpartum haemorrhage. Model 4 showed that a maximum dose of oxytocin ≥ 20 mU/min was associated with postpartum haemorrhage both for those augmented < 4.5 h and for those augmented ≥ 4.5 h. Duration of labour was associated with postpartum haemorrhage in all models if lasting ≥ 16 h. KEY CONCLUSIONS: We found both oxytocin augmentation and labour duration to be associated with postpartum haemorrhage. Oxytocin doses of ≥ 20 mU/min and a labour duration of ≥ 16 h showed an independent association. IMPLICATION FOR PRACTICE: The potent drug oxytocin should be carefully administered, as doses of ≥ 20 mU/min were associated with an increased risk of PPH, regardless of the duration of oxytocin augmentation.

Induction of labor in twin pregnancies - A retrospective cohort study.

OBJECTIVE: To investigate outcomes in spontaneous and induced twin deliveries. Secondary aims were to study impact of delivery interval and breech presentation of the first twin. METHODS: This retrospective cohort study comprised 354 twin deliveries at a tertiary Norwegian hospital. Spontaneous labor onset and induction of labor were compared in women with planned vaginal delivery and gestational age ≥ 34 weeks. The main outcome was intrapartum cesarean section. Secondary outcomes were umbilical arterial pH and five-minute Apgar scores. RESULTS: Among the induced labors, 63/229 (27.5%) women underwent intrapartum cesarean section, compared to 45/125 (36%) in spontaneous labors (P = 0.10). Odds ratio for intrapartum cesarean section in induced labors was 0.65 (95% CI 0.40-1.04) after adjusting for maternal age and parity. Median umbilical arterial pH was significantly lower in the second twins in both spontaneous and induced labors, 7.28 (6.94-7.43) vs. 7.32 (7.16-7.42), and 7.27 (6.90-7.48) vs. 7.29 (7.08-7.45), respectively. pH < 7.00 rarely occurred. Second twins born after a delivery interval > 30 min had a significantly higher frequency of pH < 7.10 than those with a shorter interval, P < 0.01. No significant difference was found in frequency of pH < 7.10 between breech-presenting and cephalic-presenting first twins (P = 0.65). One unexpected intrapartum fetal death occurred after labor induction. CONCLUSION: Our results support spontaneous onset and induction of labor as safe. Intrapartum cesarean section rates did not differ significantly between spontaneous and induced labors. Delivery interval > 30 min was associated with a lower pH in the second twin.

Put your weight behind it-Effect of body mass index on the active second stage of labour: A retrospective cohort study.

OBJECTIVE: To explore the duration of the active phase of the second stage of labour in relation to maternal pre-pregnant body mass index (BMI). DESIGN: Retrospective cohort study. SETTING: Labour wards of three Norwegian university hospitals, 2012-2019. POPULATION: Nulliparous and parous women without previous caesarean section with a live singleton fetus in cephalic presentation and spontaneous onset of labour, corresponding to the Ten Group Classification System (TGCS) group 1 and 3. METHODS: Women were stratified to BMI groups according to WHO classification, and estimated median duration of the active phase of the second stage of labour was calculated using survival analyses. Caesarean sections and operative vaginal deliveries during the active phase were censored. MAIN OUTCOME MEASURES: Estimated median duration of the active phase of second stage of labour. RESULTS: In all, 47 942 women were included in the survival analyses. Increasing BMI was associated with shorter estimated median duration of the active second stage in both TGCS groups. In TGCS group 1, the estimated median durations (interquartile range) were 44 (26-75), 43 (25-71), 39 (22-70), 33 (18-63), 34 (19-54) and 29 (16-56) minutes in BMI groups 1-6, respectively. In TGCS group 3, the corresponding values were 11 (6-19), 10 (6-17), 10 (6-16), 9 (5-15), 8 (5-13) and 7 (4-11) minutes. Increasing BMI remained associated with shorter estimated median duration in analyses stratified by oxytocin augmentation and epidural analgesia. CONCLUSION: Increasing BMI was associated with shorter estimated median duration of the active second stage of labour.

Trisomy 21 - incidence, diagnostics and pregnancy terminations 1999-2018. / Trisomi 21 ­ insidens, diagnostikk og svangerskapsavbrudd 1999­2018.

BACKGROUND: We hypothesised that the examinations offered to pregnant women at fetal medicine centres differ from those offered to other pregnant women in Norway. We therefore wanted to investigate the incidence, prenatal diagnostics and pregnancy terminations in cases of trisomy 21. We also wanted to compare the figures from the National Center for Fetal Medicine, St Olav's Hospital, Trondheim University Hospital, with national figures for Norway. MATERIAL AND METHOD: We analysed figures for the period 1999-2018 retrospectively. National data were compared with an unselected population whose local hospital is St Olav's Hospital. National figures were retrieved from the Medical Birth Registry of Norway and local figures were from the quality registry at the National Center for Fetal Medicine. RESULTS: The national incidence of trisomy 21 was 0.20 %, varying from 0.14 % to 0.23 %, and showed a significant increase over time (p < 0.01). The increasing incidence showed an association with increasing age in the women (p < 0.01). The incidence of live births was stable, even though the proportion of pregnancy terminations increased. In the local population, the incidence of trisomy 21 was 0.19 %. A total of 68.2 % of the local population were diagnosed prenatally, and 87.7 % of these pregnant women terminated the pregnancy. There was a significantly higher proportion of pregnancy terminations in the local population than in the remainder of the national population (p < 0.01). INTERPRETATION: The difference in the proportion of pregnancy terminations may be associated with variation in access to prenatal diagnostics.

Intrapartum ultrasound in women with prolonged first stage of labor.

The first stage of labor is from the start of active labor until the cervix is fully dilatated. To assess labor progress during this stage, a clinical examination has traditionally been done. The cervical dilatation, fetal head position, and fetal head station are evaluated. Moreover, these observations can be made with an ultrasound examination. Studies have shown that traditional clinical examinations are subjective, have poor reproducibility, and are unreliable. Ultrasound examinations of the fetal head station and fetal head position in the first stage of labor might predict labor outcome and mode of delivery and can help in decision making when prolonged first stage of labor is diagnosed.

There are 4, not 7, cardinal movements in labor.

The mechanics of labor describe the forces required for fetal descent, and the movements that the fetus must perform to overcome the resistance met by the maternal bony pelvis and soft tissue. The fetus negotiates the birth canal and rotational movements are necessary for descent. Anglo-American literature lists 7 cardinal movements, namely engagement, descent, flexion, internal rotation, extension, external rotation, and expulsion. German and older English literature lists only 4 rotational movements as the cardinal movements and excludes engagement, descent, and expulsion. We would argue that descent is the main purpose of the uterine powers and cardinal movements, a description of the rotational movements the fetal head and shoulders must perform to obtain descent. Ultrasound offers a historically unique opportunity for noninvasive, dynamic studies of the mechanics of labor. The information gathered by clinical examination and ultrasound should be integrated into clinical decision making.

Induction of labor in breech presentations - a retrospective cohort study.

INTRODUCTION: There is limited evidence on the safety and outcome of induction of breech labor. In this study, we aimed to compare the outcomes of spontaneous and induced breech deliveries and to describe variations in induction rates. MATERIAL AND METHODS: This was a retrospective cohort study comprising 1054 singleton live fetuses in breech presentation at Trondheim University Hospital from 2012 to 2019. The main outcome was intrapartum cesarean section, and secondary outcomes were postpartum hemorrhage, anal sphincter ruptures, Apgar scores, pH in the umbilical artery, and metabolic acidosis. All data were obtained from the hospital birth journal. RESULTS: Induction of labor was performed in 127/606 (21.0%) women with planned vaginal birth. The frequency of intrapartum cesarean section was 48.0% for induced labor vs 45.7% for spontaneous labor (P = .64). We found no differences in the frequency of postpartum hemorrhage or anal sphincter ruptures between induced and spontaneous births. The median pH in the umbilical artery was significantly lower in neonates with induced labor compared with neonates with spontaneous labor (7.22 vs 7.25; P = .02). The frequency of pH <7.05 was 7.0% for induced labor vs 2.9% (P = .05) for spontaneous labor, but the frequency of pH <7.0 was not significantly different: 2.6% vs 0.8% (P = .14), respectively. Three neonates with planned vaginal birth had metabolic acidosis: two with spontaneous labors and one with induced labor. Three fetuses with planned vaginal birth died during labor: two with spontaneous onset of labor and one with induced labor. All three were extremely preterm: two were delivered in week 23 and one in week 25. We did not observe any significant trend in induction rates in either parous or nulliparous women. CONCLUSIONS: The induction rates were stable during the study period. We did not observe any significant difference in intrapartum cesarean section rates, in the frequency of pH <7.0 in the umbilical artery, or in the frequency of metabolic acidosis when comparing induced and spontaneous breech deliveries.

Structured clinical examinations in labor: rekindling the craft of obstetrics.

OBJECTIVES: Exact knowledge of fetal station and position is of paramount importance for reliable surveillance of labor progress and a prerequisite for safe operative vaginal procedures. Detailed clinical assessments are thoroughly described in old textbooks, but almost forgotten in contemporary obstetrics. Ultrasound is suggested as an objective diagnostic tool in active labor. Several publications have demonstrated a low correlation between ultrasound and clinical assessment of fetal head station and position, but the methods of clinical assessment in these studies are poorly described. We wanted to explore if a quality clinical assessment could perform better than clinical assessment in previous publications, by analyzing the correlation between a structured method of clinical assessment and intrapartum ultrasound. METHODS: In all, 100 laboring women with cervical dilatation ≥7 cm were included in a prospective cohort study at Oslo University Hospital-Ullevål from October to December 2016. The study design was cross-sectional. Clinical examinations were performed by one special educated consultant (JKI), and transabdominal and transperineal ultrasound clips were recorded and examined by a blinded expert in intrapartum ultrasound (TME). Fetal position was classified as a clock face with 12 units (hourly divisions) and thereafter categorized as occiput anterior (OA), left occiput transverse (LOT), occiput posterior (OP), and right occiput transverse (ROT) positions. Fetal station was categorized clinically from -5 to +5 and measured with ultrasound as angle of progression (AoP) and head-perineum distance (HPD). AoP is the angle between a longitudinal line through the symphysis and a tangent to the head contour. HPD is the shortest distance between the fetal skull and the perineum. RESULTS: Eight women were excluded due to strong contractions between clinical assessments and ultrasound measurements, fetal distress, or incomplete examinations. Fetal position assessed with ultrasound and clinical examination agreed exactly in 48/92 (52%) of cases, within one unit (hour) in 87/92 (95%) of cases and within two units in 90/92 (98%) of cases. It differed by three units in one case and by five units in one case. The agreement categorized into OA, LOT, OP, and ROT was good (Cohen's kappa 0.72; 95% CI 0.61-0.84). For station, the agreement was very good for both HPD (Pearson correlation coefficient r = 0.86; 95% CI 0.80-0.91) and AoP (r = 0.77; 95% CI to 0.67-0.84). The correlation between HPD and AoP was good (r = 0.76; 95% CI 0.65-0.84). CONCLUSION: We found very good correlations between structured clinical assessments and ultrasound examinations, suggesting that an objective quality in clinical examinations is possible to achieve. More focus on clinical skills training may improve accuracy for clinicians.

Fetal molding examined with transperineal ultrasound and associations with position and delivery mode.

BACKGROUND: To accommodate passage through the birth canal, the fetal skull is compressed and reshaped, a phenomenon known as molding. The fetal skull bones are separated by membranous sutures that facilitate compression and overlap, resulting in a reduced diameter. This increases the probability of a successful vaginal delivery. Fetal position, presentation, station, and attitude can be examined with ultrasound, but fetal head molding has not been previously studied with ultrasound. OBJECTIVE: This study aimed to describe ultrasound-assessed fetal head molding in a population of nulliparous women with slow progress in the second stage of labor and to study associations with fetal position and delivery mode. STUDY DESIGN: This was a secondary analysis of a population comprising 150 nulliparous women with a single fetus in cephalic presentation, with slow progress in the active second stage with pushing. Women were eligible for the study when an operative intervention was considered by the clinician. Molding was examined in stored transperineal two-dimensional and three-dimensional acquisitions and differentiated into occipitoparietal molding along the lambdoidal sutures, frontoparietal molding along the coronal sutures, and parietoparietal molding at the sagittal suture (molding in the midline). Molding could not be classified if positions were unknown, and these cases were excluded. We measured the distance from the molding to the head midline, molding step, and overlap of skull bones and looked for associations with fetal position and delivery mode. The responsible clinicians were blinded to the ultrasound findings. RESULTS: Six cases with unknown position were excluded, leaving 144 women in the study population. Fetal position was anterior in 117 cases, transverse in 12 cases, and posterior in 15 cases. Molding was observed in 79 of 144 (55%) fetuses. Molding was seen significantly more often in occiput anterior positions than in non-occiput anterior positions (69 of 117 [59%] vs 10 of 27 [37%]; P=.04). In occiput anterior positions, the molding was seen as occipitoparietal molding in 68 of 69 cases and as parietoparietal molding in 1 case with deflexed attitude. Molding was seen in 19 of 38 (50%) of occiput anterior positions ending with spontaneous delivery, 42 of 71(59%) ending with vacuum extraction, and in 7 of 8 (88%) with failed vacuum extraction (P=.13). In 4 fetuses with occiput posterior positions, parietoparietal molding was diagnosed, and successful vacuum extraction occurred in 3 cases and failed extraction in 1. Frontoparietal molding was seen in 2 transverse positions and 4 posterior positions. One delivered spontaneously; vacuum extraction failed in 3 cases and was successful in 2. Only 1 of 11 fetuses with either parietoparietal or frontoparietal molding was delivered spontaneously. CONCLUSION: The different types of molding can be classified with ultrasound. Occipitoparietal molding was commonly seen in occiput anterior positions and not significantly associated with delivery mode. Frontoparietal and parietoparietal moldings were less frequent than reported in old studies and should be studied in larger populations with mixed ethnicities.

The Labour Progression Study (LaPS): Duration of labour following Zhang's guideline and the WHO partograph - A cluster randomised trial.

OBJECTIVE: To investigate labour duration in different phases of labour when adhering to Zhang's guideline for labour progression compared with the WHO partograph. DESIGN: A secondary analysis of a cluster randomised controlled trial. SETTING: Fourteen Norwegian birth care units, each with more than 500 deliveries per year constituted the clusters. PARTICIPANTS: A total of 7277 nulliparous women with singleton foetus in a cephalic presentation and spontaneous onset of labour at term were included. INTERVENTION: Seven clusters were randomised to the intervention group that adhered to Zhang's guideline (n = 3972) and seven to the control group that adhered to the WHO partograph (n = 3305) for labour progression. MEASUREMENTS: The duration of labour from the first registration of cervical dilatation (≥ 4 cm) to the delivery of the baby and the duration of the first and second stages of labour; the time-to-event analysis was used to compare the duration of labour between the two groups after adjusting for baseline covariates. FINDINGS: The adjusted median duration of labour was 7.0 h in the Zhang group, compared with 6.2 h in the WHO group; the median difference was 0.84 h with 95% confidence interval [CI] (0.2-1.5). The adjusted median duration of the first stage was 5.6 h in the Zhang group compared with 4.9 h in the WHO group; the median difference was 0.66 h with 95% CI (0.1-1.2). The corresponding adjusted median duration of the second stage was 88 and 77 min; the median difference was 0.18 h with 95% CI (0.1-0.3). KEY CONCLUSIONS: The women who adhered to Zhang's guideline had longer overall duration and duration of the first and second stages of labour than women who adhered to the WHO partograph. IMPLICATIONS FOR PRACTICE: Understanding the variations in the duration of labour is of great importance, and the results offer useful insights into the different labour progression guidelines, which can inform clinical practice.

Incidence and risk factors for obstetric anal sphincter ruptures, OASIS, following the introduction of preventive interventions. A retrospective cohort study from a Norwegian hospital 2012-2017.

OBJECTIVE: A decrease of obstetric anal sphincter injuries (OASIS) was observed after preventive interventions were implemented at a Norwegian university hospital. The aim was to investigate whether the improvement had sustained over the following years. MATERIALS AND METHODS: We performed a retrospective cohort study of 18 258 singleton vaginal cephalic births, ≥37 + 0 weeks of gestation during 2012-2017, examining data from the hospital's birth journals and separate registration forms. Interventions to prevent OASIS were implemented in 2011, and training in practical skills was repeated each year. MAIN OUTCOME MEASURES: The main outcome was OASIS (n = 377). RESULTS: Frequency of OASIS overall decreased from 3.6% prior to 2011 to 2.1% after the intervention and sustained at that level throughout the study period. A trend of fewer OASIS among spontaneous deliveries, decreasing from 2.1% to 1.2% (p = 0.01) was observed, but no trend was seen for instrumental deliveries (p = 0.37), where the incidence fluctuated between 4.0% and 9.3% with an average of 6.5%. Primiparity, increased maternal age and increased fetal head circumference were associated with more OASIS in spontaneous deliveries. In instrumental deliveries, primiparity, occiput posterior position and increased fetal head circumference were associated with more OASIS, whilst episiotomy was associated with fewer OASIS. CONCLUSION: The incidence of obstetric anal sphincter injuries maintained at a similar level of around 2.1% during the six following years after introducing preventive interventions. Regularly repetition and practical training seemed to be effective.

The Labor Progression Study: The use of oxytocin augmentation during labor following Zhang's guideline and the WHO partograph in a cluster randomized trial.

INTRODUCTION: This study aims to investigate the use of oxytocin augmentation during labor in nulliparous women following Zhang's guideline or the WHO partograph. MATERIAL AND METHODS: This is a secondary analysis of a cluster randomized controlled trial in 14 birth-care units in Norway, randomly assigned to either the intervention group, which followed Zhang's guideline, or to the control group, which followed the WHO partograph, for labor progression. The participants were nulliparous women who had a singleton full-term fetus in a cephalic presentation and spontaneous onset of labor, denoted as group 1 in the Ten Group Classification System. RESULTS: Between December 2014 and January 2017, 7277 participants were included. A total of 3219 women (44%) received augmentation with oxytocin during labor. Oxytocin was used in 1658 (42%) women in the Zhang group compared with 1561 (47%) women in the WHO group. The adjusted relative risk for augmentation with oxytocin was 0.98 (95% CI 0.84-1.15; P = .8) in the Zhang vs WHO group, with an adjusted risk difference of -0.8% (95% CI -7.8 to 6.1). The participants in the Zhang group were less likely to be augmented with oxytocin before reaching 6 cm of cervical dilatation (24%) compared with participants in the WHO group (28%), with an adjusted relative risk of 0.84 (95% CI 0.75-0.94; P = .003). Oxytocin was administered for almost 20 min longer in the Zhang group than in the WHO group, with an adjusted mean difference of 17.9 min (95% CI 2.7-33.1; P = .021). In addition, 19% of the women in the Zhang group and 23% in the WHO group received augmentation with oxytocin without being diagnosed with labor dystocia. CONCLUSIONS: Although no significant difference in the proportion of oxytocin augmentation was observed between the 2 study groups, there were differences in how oxytocin was used. Women in the Zhang group were less likely to receive oxytocin augmentation before 6 cm of cervical dilatation. The duration of augmentation with oxytocin was longer in the Zhang group than in the WHO group.

Correlation Between Fetal Weight Gain and Birth Weight with Blood Flow in the Uterine Arteries Calculated with the PixelFlux Technique.

INTRODUCTION: The aim was to investigate correlations between fetal weight gain/day and birthweight with blood flow estimates in the uterine arteries calculated with the PixelFlux technique and with measurements from TAmax. We also aimed to examine the agreement between estimates using the two methods. MATERIAL AND METHODS: We conducted a prospective observational pilot study in pregnancy week 24-25 in women with risk pregnancies referred to the fetal medical centre at St. Olavs Hospital, Trondheim, Norway from March 2016 to June 2016. Blood flow in the uterine arteries was calculated using time-averaged peak velocity (TAmax) and the PixelFlux technique. PixelFlux is a method based on pixelwise calculation of spatially angle-corrected velocities and areas of all pixels inside a vessel during a heart cycle. RESULTS: The mean flow calculated from PixelFlux and TAmax was 811 ml/minute and 787 ml/minute, respectively. The intra-class correlation coefficient was 0.83 (95% CI 0.72-0.90) and limits of agreement were -441 ml/minute (95% CI -558 to -324 ml/minute) to 489 ml/minute (95% CI 372 to 606 ml/minute). We observed a significant correlation between mean flow calculated from PixelFlux and birthweight (r=0.41; p<0.01) and between flow calculated from PixelFlux and weight gain/day (r=0.33; p=0.02). Calculation based on TAmax was significant correlated to birthweight (r=0.34; p=0.02), but not to weight-gain/day. Pulsatile index was not correlated to flow, birthweight or fetal weight-gain/day. CONCLUSIONS: We found significant correlations between estimated blood flow in the uterine arteries using the PixelFlux technique with fetal weight-gain/day and with birthweight. Estimates from two methods showed good agreement.

Study protocol: the Labor Progression Study, LAPS - does the use of a dynamic progression guideline in labor reduce the rate of intrapartum cesarean sections in nulliparous women? A multicenter, cluster randomized trial in Norway.

BACKGROUND: The increasing rate of intrapartum cesarean sections is subject of attention and concern as it is associated with adverse outcomes. Labor dystocia is one of the most frequent indications for cesarean sections even though there is no consensus on criteria for labor dystocia. Traditionally the progression of labor follows guidelines based on Friedman's curve from the mid 1950s. In 2010 Zhang presented a new labor curve and a dynamic guideline for labor progression based on contemporary research. The main aim of this trial is to evaluate whether adhering to Zhang's guideline for labor progression, changes the intrapartum cesarean section rate in nulliparous women without jeopardising maternal and neonatal outcomes compared to a traditional guide line called the 4-h action line based on Friedman's curve. METHODS/DESIGN: A multicenter cluster randomized trial including 14 birth care units in Norway is conducted. Seven units are randomized to use the 4-h action line guideline for labor progression and seven units are randomized to use Zhang's new dynamic guideline for labor progression, for all nulliparous women with a singleton fetus in a cephalic presentation and spontaneous onset of labor at term. Clinical outcomes are compared between the groups. The determination of the sample size (number of clusters and individuals) is based on a power calculation of intrapartum cesarean section, which is 9.2% in the study population (p1). Further, we expect that the intrapartum cesarean section rate will be 6.7% (p2) which is a 25% reduction, when using the new guideline. With a chosen significance level of 0.05, a power of 80% and p1 = 9.2% and p2 = 6.9%, we should include at least 14 clusters and 6582 individuals. DISCUSSION: Clinical consequences when using the guideline by Zhang have, to the best of our knowledge, not been investigated earlier. The results will provide a strong basis to make a qualified decision on whether it is beneficial to introduce a dynamic labor progression curve in contemporary obstetrics both nationally and internationally. TRIAL REGISTRATION: Clinicaltrials, NCT02221427.

Variability Over Time of Normal-Sized Fetal Renal Pelvis During the Second Trimester Scan.

PURPOSE: To investigate the variability of the normal-sized fetal renal pelvis (≤5 mm) over time and to analyze repeatability of measurements. MATERIALS AND METHODS: 98 fetal renal pelvises and 49 fetal urinary bladders were analyzed at a gestational age of 17-20 weeks at St. Olavs Hospital, Trondheim, Norway. The anterior-posterior diameter (APD) of the fetal renal pelvis and two diameters of the fetal bladder were measured with an interval of at least 30 min. Intra- and interobserver variations and variations over time and in association with bladder size were investigated. RESULTS: The mean difference in renal pelvis size between the first and second measurements was 0.09 mm (95% CI, -0.09 to 0.26 mm). The variation over time was ≤1 mm in 85% of cases and the renal pelvis was ≤4 mm in both the first and second examinations in 92% of cases. The intraclass correlation coefficient (ICC) was 0.54 (95% CI: 0.31 to 0.69). We did not observe any association between variation of bladder size and variation of APD. The difference in fetal renal pelvis size was ≤1 mm in 70% of observations for the first examiner and 58% for the second examiner. The intraobserver ICCs were 0.71 (95% CI: 0.62-0.78) and 0.60 (95% CI: 0.50-0.70) for the two observers respectively. The interobserver difference was ≤1 mm in 72% of cases and the interobserver ICC was 0.56 (95% CI: 0.34-0.71). CONCLUSION: The variation of the APD of the fetal renal pelvis over time was small in fetuses with the APD in the lower range and can mainly be explained by intraobserver variation.