Fetal Doppler reference values in women with a normal body mass index

Objectives: To construct gestation specific reference limits for fetal umbilical (UA), middle cerebral artery (MCA) pulsatility indices (PI) and the cerebroplacental ratio (CPR) in singleton pregnancies with normal BMI between 16 and 40 weeks of gestation. Methods: We ultrasonographically examined 596 fetuses from women with normal nutritional and health status and minimal environmental constraints on fetal growth. Each mother was considered only once for measurement of fetal Doppler indices, at gestations between 16 and 40 weeks in a prospective cross-sectional study. Gestational age was confirmed by fetal crown-rump length measurement between 11 and 14 weeks. Pulsatility indices of umbilical and middle cerebral arteries were measured by real time and Doppler ultrasonography. CPR ratio was calculated by dividing MCA PI by UA PI. The fetal Doppler measurements obtained from the current study were compared with commonly used reference charts. For each parameter separate polynomial regression models were fitted to estimate the gestation specific means and standard deviations, assuming that the measurements have a normal distribution at each gestational age. Results: A significant difference of fetal Doppler indices was observed between our study and previously published reference charts for most gestational weeks. The fitted 10th, 50th and 90th centiles at 40 weeks of gestation were 0.65, 0.87 and 1.08 for UA PI; 0.93, 1.32 and 1.71 MCA PI; 1.02, 1.58 and 2.13 for CPR. Conclusions: These charts can be used for better defining the normal range of fetal arterial Doppler indices. This will be useful in the diagnosis and management of fetuses with abnormal fetal growth.

Comparison of ultrasound fetal biometry of singleton fetuses with a reference chart in pregnant women with normal nutritional and health status

Objetives: The aim of this study was to compare fetal biometry of singleton fetuses in pregnant women with normal nutritional and health status in the Ampara district, with a commonly used reference chart. Methods: A cross sectional study was carried out in the Ampara District. Women with normal nutritional and health status and minimal environmental constraints on fetal growth (n=714) were enrolled during the first trimester and gestational age was confirmed by fetal crown-rump length measurement between 11 weeks + 0 days and 13 weeks + 6 days. For this study, each mother was considered only once for measurement of fetal biometry, at gestations between 11 and 41 weeks. Fetal bi-parietal diameter (BPD), head circumference (HC), abdominal circumference (AC) and femur length (FL) were measured using standard techniques, and separate regression models were fitted to estimate the means and standard deviations and derive gestation specific centiles for each parameter, assuming that the measurements have a normal distribution at each gestational age. The fetal biometry results obtained from the current study were compared with a commonly used reference chart. Results: The fitted 10th, 50th and 90th centiles at 40 weeks of gestation were, 87.9 mm, 93.2 mm and 98.5 mm for BPD, 313.8 mm, 328.9 mm and 344.0 mm for HC; 298.2 mm, 322.5 mm and 346.9 mm for AC and 69.7 mm, 75.0 mm and 80.2 mm for FL. When compared with the reference chart, significant differences of fetal biometry were seen in the third trimester but not in the second trimester. Conclusions: Ultrasound fetal biometry of singleton fetuses in pregnant women with normal nutritional and health status in the Ampara District were significantly different in the third trimester, from a routinely used reference chart.

Symphysis-pubis fundal height charts to assess fetal size in women with a normal body mass index.

OBJECTIVES: To construct symphysis-pubis fundal height (SFH) charts to estimate fetal size in pregnant women with a normal body mass index (BMI) and to describe the variation of SFH measurements according to BMI. METHODS: cross sectional study was carried out at Ampara and Gampaha Districts in Sri Lanka. Women with normal nutritional and health status, normal BMI and minimal environmental constraints on fetal growth, with ultra sound confirmation of dates by fetal crown-rump length measurements between 11 weeks and 13 weeks + six days,had their SFH measured, using non-elastic tape and standard techniques, between 24 and 41 weeks gestation. Only one measurement of SFH was obtained from each pregnant woman. Linear and polynomial regression models were fitted separately to the means and standard deviations (SD) as functions of gestational age to identify the model with the best fit. Centiles were derived from the mean and SD at each gestational age. RESULTS: Pregnant women from the districts of Ampara (n=387) and Gampaha (n=200) were recruited. Other than a difference of -1.5 cm (95% CI -2.27 to -0.23) at 38 weeks of gestation, there were no significant differences between the SFH measurements obtained from women with normal BMI in Ampara and Gampaha Districts. Using the SFH measurements from the Ampara sample, charts were created for 10th, 50th and 90th centile values of SFH. At 40 weeks of gestation these were 34 cm, 37 cm and 41 cm respectively. At 40 weeks gestation, the variation in SFH measurements between BMI sub groups within the normal range was approximately 1.4 cm to 1.6 cm. CONCLUSIONS: These SFH charts could be used to estimate fetal size in pregnant women with normal BMI.

Use of ultrasound in predicting success of intrauterine contraceptive device insertion immediately after delivery.

OBJECTIVES: To assess by ultrasound examination the success of insertion of an intrauterine contraceptive device (IUD) immediately after delivery and to determine the optimal distance between the lower end of the IUD and the internal os in predicting successful retention of an IUD. METHODS: This was a prospective study carried out between December 2012 and April 2013. Two ultrasound examinations, transabdominal and transvaginal, were performed prior to hospital discharge following delivery and again at 6 weeks following delivery in women who received a postpartum IUD. Distance from the internal os to the lower end of the IUD was measured at each examination and compared in unsuccessful and successful cases of postvaginal delivery (PVD) and post-Cesarean section (PCS) IUD insertion. Logistic regression and receiver-operating characteristics (ROC) curve analysis were used to determine the difference in success between the two modes of delivery and to determine the optimal cut-off of the internal os-to-IUD distance for successful retention, respectively. RESULTS: Ninety-one women were included in the study, comprising 60 PVD and 31 PCS IUD insertions. Thirteen PVD (22.4%) and eight PCS (25.8%) IUDs were either expelled spontaneously or removed at the 6-week scan because of improper placement. Mean distance from the internal os to the lower end of the IUD on ultrasound examination immediately after insertion was significantly greater in successful cases than in those in which IUDs were subsequently expelled/displaced (mean difference after PVD insertion, 20.1 mm (P = 0.006); mean difference after PCS insertion, 10.3 mm (P = 0.05)). Logistic regression analysis demonstrated that mode of delivery was not independently associated with successful retention of the IUD (P = 0.72; OR, 0.831 (95% CI, 0.301-2.189)). The distance from the lower end of the IUD to the internal os measured at ultrasound examination prior to hospital discharge provided reasonable predictive accuracy for determining retention of the IUD, with an area under the ROC curve of 0.74 (95% CI, 0.60-0.88) and an optimal cut-off of ≥ 30 mm (sensitivity, 64.71% (95% CI, 52.17-75.92%) and specificity, 80.95% (95% CI, 58.09-94.55%)). CONCLUSIONS: IUD insertion immediately postpartum is feasible but carries a substantial risk of unsuccessful IUD retention. Ultrasound examination after insertion of an IUD could be considered for predicting the success of IUD retention.

Risk of stillbirth at term and optimum timing of delivery in uncomplicated south Asian singleton pregnancies.

OBJECTIVES: Aims of this study were to compare the perinatal mortality rate and the prospective risk of stillbirth for each given gestational age and to ascertain whether it is safe to continue the pregnancy beyond 40 weeks of gestational age and induce labour at 41 weeks in low risk singleton pregnancies. METHODS: This was a retrospective study. The perinatal mortality and prospective risk were calculated per 1000 total births and 1000 ongoing pregnancies respectively in well dated singleton pregnancies. 38+0 to 39+6 gestational age was taken as the reference. RESULTS: A total of 12,595 deliveries after 28 weeks of gestation were included. The risk of stillbirth at 38+0 to 39+6 weeks was 1.43 (95% CI, 0.9 to 2.4) per 1000 on going pregnancies. The perinatal mortality rate at 38+0 to 39+6 weeks was 2.9 (95% CI, 1.9 to 4.5) per 1000 total births. The perinatal mortality rate decreased throughout gestation and it was lowest at 40+0 - 41+6. In contrast, risk of stillbirth increased with advancing gestation and peaked at 40+0 - 41+6 (2.57, 95% CI, 1.4 to 4.7). However, risk of stillbirth at 40+0 - 41+6 was not statistically different from 38+0 to 39+6 (OR 1.79, 95% CI, 0.80 to 3.98). To prevent one stillbirth, 886 pregnancies should be induced at 38+0 to 39+6. CONCLUSIONS: Risk of stillbirth is more informative than perinatal mortality at term. Frequent antenatal fetal surveillance should be adopted towards term in order to identify high risk pregnancies. Elective delivery before 40 weeks in low risk pregnancies is not justified.

Accuracy of ultrasound estimated fetal weight formulae to predict actual birthweight after 34 weeks: prospective validation study.

OBJECTIVES: Late onset fetal growth restriction is often missed and is responsible for most intrauterine deaths. Ultrasound fetal biometry is routinely used to calculate estimated fetal weight (EFW). The aim of this study was to determine the accuracy of established ultrasound EFW formulae to identify small and large for gestational age fetuses when used after 35 weeks gestation. METHODS: This was a prospective validation study done between January 2012 and July 2012 at General Hospital Ampara. An ultrasound examination was performed and fetal biometry was documented within one week before the delivery in well dated pregnancies. The mean of the differences between ultrasound EFW derived from 9 formulae and true birthweight and their standard error of mean (SE) were calculated for each formula. Systematic measurement error was assumed to exist if zero lay outside the mean difference ± 2SE. To show the EFW frequency distribution, z-scores were calculated as the number of standard deviations an observed EFW measurement deviated from the mean for gestation. RESULTS: A total of 393 pregnancies at gestational age between 35 and 41 weeks were recruited. Mean gestational age at the ultra sound scan was 39.36 weeks SD (1.05). All EFW formulae either under or over estimated the birthweight in singleton pregnancies. Almost all the formulae overestimated the fetal weight in low birthweight babies whilst underestimating the fetal weight in birthweight >3500g. Campbell formula remained the only EFW formula without systematic error when measuring babies between 2500g and 3500g. None of the EFW z-scores were normally distributed. CONCLUSIONS: This study found that all routinely used EFW formulae would either over or under estimate the fetal weight. Until an optimum EFW formula that suits the Sri Lankan population is determined, interpretation of ultrasound EFW should be done cautiously, especially in small for gestational age babies.

Sri Lankan fetal/ birthweight charts: validation of global reference for fetal weight and birthweight percentiles.

INTRODUCTION: Small for gestational age (SGA) is defined as birthweight below the tenth centile at a particular gestational week. Birthweight centiles for different populations are varied. Generic reference for fetal weight and birthweight that could be adapted to local populations was recently described. The purpose of this study was to validate the reference for birthweights adapted to the local population. METHODS: This was a prospective validation study done between January 2012 and July 2012 in well dated pregnancies at General Hospital, Ampara. Observed frequencies of birthweights of 5th, 10th, 50th, 90th and 95th percentiles for Hadlock formula, World Health Organization (WHO) global survey data for Sri Lanka and India were calculated. The expected frequencies for each birthweight centile of our study were compared with observed frequencies. RESULTS: A total of 411 patients were recruited and 207 delivered at 40 weeks (40+0-40+6). The mean birth-weight (SD) at 40 weeks of gestation was 3140g (432g). Hadlock formula and WHO reference data for India overestimate and underestimate most of the birthweights respectively. WHO generic reference adapted to Sri Lanka fitted well with our data. The mean birthweight of our population is similar, and the adapted reference range would identify most of the small fetuses correctly. It would also identify almost all the babies with weight above the 90th centile. CCONCLUSIONS: The findings of the study show that the observed distribution of birthweight fitted well with the reference range derived from the WHO global reference range adapted to Sri Lankan population. WHO reference charts can be used effectively in Sri Lankan population.