How should we interpret lactate in labour? A reference study.

OBJECTIVE: To investigate maternal lactate concentrations in labour and the puerperium. DESIGN: Reference study. SETTING: Tertiary obstetric unit. POPULATION: 1279 pregnant women with good perinatal outcomes at term. METHODS: Electronic patient records were searched for women who had lactate measured on the day of delivery or in the following 24 hours, but who were subsequently found to have a very low likelihood of sepsis, based on their outcomes. MAIN OUTCOME MEASURES: The normative distribution of lactate and C-reactive protein (CRP), differences according to the mode of birth, and the proportion of results above the commonly used cut-offs (≥2 and ≥4 mmol/l). RESULTS: Lactate varied between 0.4-5.4 mmol/l (median 1.8 mmol/l, interquartile range [IQR] 1.3-2.5). It was higher in women who had vaginal deliveries than caesarean sections (median 1.9 vs. 1.6 mmol/l, pdiff  < 0.001), demonstrating the association with labour (particularly active pushing in the second stage). In contrast, CRP was more elevated in women who had caesarean sections (median 71.8 mg/l) than those who had vaginal deliveries (33.4 mg/l, pdiff  < 0.001). In total, 40.8% had a lactate ≥2 mmol/l, but 95.3% were <4 mmol/l. CONCLUSIONS: Lactate in labour and the puerperium is commonly elevated above the levels expected in healthy pregnant or non-pregnant women. There is a paucity of evidence to support using lactate or CRP to make decisions about antibiotics around the time of delivery but, as lactate is rarely higher than 4 mmol/l, this upper limit may still represent a useful severity marker for the investigation and management of sepsis in labour.

Improving diagnostic accuracy in pregnancy with individualised, gestational age-specific reference intervals.

BACKGROUND AND AIMS: Investigations in pregnancy should be interpreted using pregnancy-specific reference intervals (RIs). However, because of the progressive nature of pregnancy, even pregnancy-specific RIs may not be equally representative at different gestations. We proposed that gestational age-specific RIs may increase diagnostic accuracy over those with fixed limits. MATERIALS AND METHODS: The trajectory of platelets was mapped in 32,778 pregnant women, using 116,798 results. Then we evaluated the accuracy with which a low measurement in early pregnancy (<3rd centile) predicted thrombocytopaenia at term, compared to the existing limit (<150 × 109/L). RESULTS: Platelets fell by 14.8% between 8 and 40 weeks. Platelets below the 3rd centile before 20 weeks predicted thrombocytopaenia at term (<100 × 109/L) with a significantly greater degree of accuracy than a fixed limit (AUC 0.86 vs. 0.76, p = 0.004). CONCLUSION: Pregnancy-specific RIs can be defined using routinely collected hospital data, and the abundance of such freely available data enables a detailed investigation of temporal changes throughout gestation. Individualised RIs offer improved accuracy profiles, over and above those already derived specifically from pregnant populations. Clinicians should consider how this may be used to improve diagnostic accuracy for biomarkers used in current clinical practice, and those yet to be defined.

White blood cells in pregnancy: reference intervals for before and after delivery.

BACKGROUND: White blood cells (WBC) are commonly measured to investigate suspected infection and inflammation in pregnant women, but the pregnancy-specific reference interval is variably reported, increasing diagnostic uncertainty in this high-risk population. It is essential that clinicians can interpret WBC results in the context of normal pregnant physiology, given the huge global burden of infection on maternal mortality. METHODS: We performed a longitudinal, repeated measures population study of 24,318 pregnant women in Oxford, UK, to map the trajectory of WBC between 8-40 weeks of gestation. We defined 95% reference intervals (RI) for total WBC, neutrophils, lymphocytes, eosinophils, basophils, and monocytes for the antenatal and postnatal periods. FINDINGS: WBC were measured 80,637 times over five years. The upper reference limit for total WBC was elevated by 36% in pregnancy (RI 5.7-15.0×109/L), driven by a 55% increase in neutrophils (3.7-11.6×109/L) and 38% increase in monocytes (0.3-1.1×109/L), which remained stable between 8-40 weeks. Lymphocytes were reduced by 36% (1.0-2.9×109/L), while eosinophils and basophils were unchanged. Total WBC was elevated significantly further from the first day after birth (similar regardless of the mode of delivery), which resolved to pre-delivery levels by an average of seven days, and to pre-pregnancy levels by day 21. INTERPRETATION: There are marked changes in WBC in pregnancy, with substantial differences between cell subtypes. WBC are measured frequently in pregnant women in obstetric and non-obstetric settings, and results should be interpreted using a pregnancy-specific RI until delivery, and between days 7-21 after childbirth. FUNDING: None.

Pregnancy-specific Reference Intervals for BNP and NT-pro BNP-Changes in Natriuretic Peptides Related to Pregnancy.

CONTEXT: Cardiac disease is the leading cause of maternal mortality in the UK, so accurate cardiovascular diagnoses in pregnancy are essential. BNP (B-type natriuretic peptide) and NT-pro BNP (N-terminal-pro BNP) are useful clinical tools for investigating suspected peripartum cardiomyopathy but, as the pregnancy-specific reference intervals are undefined, it is uncertain how they should be interpreted in pregnant women. OBJECTIVES: To define trimester-specific 95% reference intervals for BNP and NT-pro BNP in pregnancy. METHODS: Longitudinal study of 260 healthy pregnant women, with sampling in each trimester. RESULTS: The upper reference limit for NT-pro BNP was 200 pg/mL in the first and second trimesters, and 150 pg/mL in the third. Levels were significantly reduced in overweight women in the third trimester (P = .0001), which supports the partitioning of reference intervals by body mass index (BMI). The upper limit for BNP was 50 pg/mL, with no detectable trimester-related differences. Although other biomarkers (hemoglobin and platelets) fell throughout pregnancy, both natriuretic peptides were initially elevated before falling by the third trimester, suggesting that the observed changes in natriuretic peptides are driven by dynamic interplay between cardiac strain and progressive hemodilution. NT-pro BNP in the first trimester was inversely associated with neonatal birthweight at term (P = .011). CONCLUSION: Cardiac biomarkers have an important role for investigating suspected disease in high-risk pregnant women, but a robust assessment of the levels expected in healthy pregnant women is an essential prerequisite to their application in clinical practice. This study has defined trimester- and BMI-specific reference intervals for NT-pro BNP and BNP, which may improve how women with suspected cardiovascular disease are investigated in pregnancy.

Pregnancy-specific reference intervals for C-reactive protein improve diagnostic accuracy for infection: A longitudinal study.

BACKGROUND AND AIMS: Infections are a major cause of maternal mortality. C-reactive protein (CRP), a commonly-used inflammatory marker, is widely used to inform diagnosis, but the upper limit of normal in pregnancy is uncertain. We have defined trimester-specific reference intervals for CRP and evaluated their diagnostic accuracy for infection. MATERIALS AND METHODS: Development cohort: longitudinal study of pregnant women to determine 95% reference intervals. Evaluation cohort: diagnostic accuracy study to evaluate these intervals in 50 women with suspected intrauterine infection. RESULTS: In these 322 healthy pregnant women, CRP was substantially higher than in most non-pregnant populations. CRP was similar in each trimester, with an upper reference limit of 19 mg/L. CRP increased linearly with body mass index (p < 0.0001). The sensitivity and specificity of CRP for diagnosing chorioamnionitis were 73% and 86%, respectively. The overall diagnostic accuracy using the pregnancy-specific reference interval was significantly better than that of the existing standard (p = 0.03). CONCLUSIONS: CRP is a widely-used clinical tool in pregnancy, and a pregnancy-specific reference interval should be used to optimise diagnostic accuracy. Chorioamnionitis was used as an example of a localised infection with well-defined outcomes, but pregnancy-specific RIs for CRP should be considered in any clinical setting including pregnant women.

Cardiac-specific troponins in uncomplicated pregnancy and pre-eclampsia: A systematic review.

BACKGROUND: The risk of myocardial infarction (MI) increases during pregnancy, particularly in women with pre-eclampsia. MI is diagnosed by measuring high blood levels of cardiac-specific troponin (cTn), although this may be elevated in women with pre-eclampsia without MI, which increases diagnostic uncertainty. It is unclear how much cTn is elevated in uncomplicated and complicated pregnancy, which may affect whether the existing reference intervals can be used in pregnant women. Previous reviews have not investigated high-sensitivity troponin in pregnancy, compared to older, less sensitive methods. METHODS: Electronic searches using the terms "troponin I" or "troponin T", and "pregnancy", "pregnancy complications" or "obstetrics". cTn levels were extracted from studies of women with uncomplicated pregnancies or pre-eclampsia. RESULTS: The search identified ten studies with 1581 women. Eight studies used contemporary methods that may be too insensitive to use reliably in this clinical setting. Two studies used high-sensitivity assays, with one reporting an elevation in troponin I (TnI) in pre-eclampsia compared to uncomplicated pregnancy, and the other only examining women with pre-eclampsia. Seven studies compared cTn between women with pre-eclampsia or uncomplicated pregnancy using any assay. Seven studies showed elevated TnI in pre-eclampsia compared to uncomplicated pregnancy or non-pregnant women. One study measured troponin T (TnT) in pregnancy but did not examine pre-eclampsia. CONCLUSION: TnI appears to be elevated in pre-eclampsia, irrespective of methodology, which may reflect the role of cardiac stress in this condition. TnI may be similar in healthy pregnant and non-pregnant women, but we found no literature reporting pregnancy-specific reference intervals using high-sensitivity tests. This limits broader application of cTn in pregnancy. There is a need to define reference intervals for cTn in pregnant women, which should involve serial sampling throughout pregnancy, with careful consideration for gestational age and body mass index, which cause dynamic changes in normal maternal physiology.

A pregnancy-specific reference interval for procalcitonin.

BACKGROUND AND AIMS: Sepsis is a leading cause of maternal death, and developing diagnostic tests for infection is increasingly important to reduce maternal mortality. The existing inflammatory markers, like C-reactive protein, are not specific for infection, which introduces diagnostic uncertainty. Procalcitonin (PCT) is used to accurately diagnose bacterial sepsis and differentiate it from other conditions, which is now particularly important given the vulnerability to COVID-19 in pregnancy. There are few studies of PCT in pregnancy as the reference interval for pregnant women is unknown. This study aimed to define the pregnancy-specific reference interval for PCT. MATERIALS AND METHODS: Cross-sectional study of 323 healthy pregnant women, with longitudinal sampling in each trimester. RESULTS: The upper reference limit for PCT was 0.05 ng/mL and did not vary materially between any observed group of gestational age, body mass index, maternal age, mean arterial blood pressure or fetal sex. CONCLUSION: Our study has shown that levels of PCT are similar in pregnant and non-pregnant populations despite the physiological changes of normal pregnancy. Therefore, pregnancy should not preclude the use of PCT in pregnant women with suspected sepsis, or for guiding antibiotic therapy in women with a diagnosed bacterial infection at any stage of pregnancy.

Maternal and neonatal outcomes in women with history of coronary artery disease.

BACKGROUND: Pregnancy outcomes in women with pre-existing coronary artery disease (CAD) are poorly described. There is a paucity of data therefore on which to base clinical management to counsel women, with regard to both maternal and neonatal outcomes. METHOD: We conducted a retrospective multicentre study of women with established CAD delivering at 16 UK specialised cardiac obstetric clinics. We included pregnancies of 24 weeks' gestation or more, delivered between January 1998 and October 2018. Data were collected on maternal cardiovascular, obstetric and neonatal events. RESULTS: 79 women who had 92 pregnancies (94 babies including two sets of twins) were identified. 35.9% had body mass index >30% and 24.3% were current smokers. 18/79 (22.8%) had prior diabetes, 27/79 (34.2%) had dyslipidaemia and 21/79 (26.2%) had hypertension. The underlying CAD was due to atherosclerosis in 52/79 (65.8%), spontaneous coronary artery dissection (SCAD) in 11/79 (13.9%), coronary artery spasm in 7/79 (8.9%) and thrombus in 9/79 (11.4%).There were six adverse cardiac events (6.6% event rate), one non-ST elevation myocardial infarction at 23 weeks' gestation, two SCAD recurrences (one at 26 weeks' gestation and one at 9 weeks' postpartum), one symptomatic deterioration in left ventricular function and two women with worsening angina. 14% of women developed pre-eclampsia, 25% delivered preterm and 25% of infants were born small for gestational age. CONCLUSION: Women with established CAD have relatively low rates of adverse cardiac events in pregnancy. Rates of adverse obstetric and neonatal events are greater, highlighting the importance of multidisciplinary care.

Maternal and fetal outcomes in pregnancies complicated by Marfan syndrome.

OBJECTIVES: Information to guide counselling and management for pregnancy in women with Marfan syndrome (MFS) is limited. We therefore conducted a UK multicentre study. METHODS: Retrospective observational study of women with MFS delivering between January 1998 and March 2018 in 12 UK centres reporting data on maternal and neonatal outcomes. RESULTS: In total, there were 258 pregnancies in 151 women with MFS (19 women had prior aortic root replacements), including 226 pregnancies ≥24 weeks (two sets of twins), 20 miscarriages and 12 pregnancy terminations. Excluding miscarriages and terminations, there were 221 live births in 139 women. Only 50% of women received preconception counselling. There were no deaths, but five women experienced aortic dissection (1.9%; one type A and four type B-one had a type B dissection at 12 weeks and subsequent termination of pregnancy). Five women required cardiac surgery postpartum. No predictors for aortic dissection could be identified. The babies of the 131 (65.8%) women taking beta-blockers were on average 316 g lighter (p<0.001). Caesarean section rates were high (50%), particularly in women with dilated aortic roots. In 55 women, echocardiographic aortic imaging was available prepregnancy and postpregnancy; there was a small but significant average increase in AoR size of 0.84 mm (Median follow-up 2.3 months) CONCLUSION: There were no maternal deaths, and the aortic dissection rate was 1.9% (mainly type B). There with no identifiable factors associated with aortic dissection in our cohort. Preconception counselling rates were low and need improvement. Aortic size measurements increased marginally following pregnancy.