Increase in ambient temperature may explain decrease in amniotic fluid index

Associations between high temperatures in pregnancy and risk of preterm birth, low birth weight, and stillbirths: systematic review and meta-analysis

OBJECTIVE

To assess whether exposure to high temperatures in pregnancy is associated with increased risk for preterm birth, low birth weight, and stillbirth.

DESIGN

Systematic review and random effects meta-analysis.

DATA SOURCES

Medline and Web of Science searched up to September 2018, updated in August 2019.

ELIGIBILITY CRITERIA FOR SELECTING STUDIES

Clinical studies on associations between high environmental temperatures, and preterm birth, birth weight, and stillbirths.

RESULTS

14 880 records and 175 full text articles were screened. 70 studies were included, set in 27 countries, seven of which were countries with low or middle income. In 40 of 47 studies, preterm births were more common at higher than lower temperatures. Exposures were classified as heatwaves, 1°C increments, and temperature threshold cutoff points. In random effects meta-analysis, odds of a preterm birth rose 1.05-fold (95% confidence interval 1.03 to 1.07) per 1°C increase in temperature and 1.16-fold (1.10 to 1.23) during heatwaves. Higher temperature was associated with reduced birth weight in 18 of 28 studies, with considerable statistical heterogeneity. Eight studies on stillbirths all showed associations between temperature and stillbirth, with stillbirths increasing 1.05-fold (1.01 to 1.08) per 1°C rise in temperature. Associations between temperature and outcomes were largest among women in lower socioeconomic groups and at age extremes. The multiple temperature metrics and lag analyses limited comparison between studies and settings.

CONCLUSIONS

Although summary effect sizes are relatively small, heat exposures are common and the outcomes are important determinants of population health. Linkages between socioeconomic status and study outcomes suggest that risks might be largest in low and middle income countries. Temperature rises with global warming could have major implications for child health.

SYSTEMATIC REVIEW REGISTRATION

PROSPERO CRD 42019140136 and CRD 42018118113.

Oligohydramnios in complicated and uncomplicated pregnancy: a systematic review and meta-analysis

OBJECTIVE

To evaluate adverse pregnancy outcomes in singleton pregnancies diagnosed with oligohydramnios through a systematic review and meta-analysis of controlled trials.

METHODS

We searched electronic databases via OVID, EBSCO, Web of Science, Google Scholar and others from 1980 to 2015. Prospective and retrospective studies with a control group were included. Two authors independently reviewed the abstracts from the literature search. Inclusion criteria were: studies in English, singleton pregnancy, normal fetal anatomy, intact membranes and oligohydramnios determined by the amniotic fluid index (AFI) technique. We stratified the meta-analysis into two groups according to risk: high risk including studies of oligohydramnios with comorbid conditions (e.g. hypertension) and low risk including studies of isolated oligohydramnios.

RESULTS

Fifteen trials met the inclusion criteria. Nine were high-risk and six were low-risk studies, including 8067 and 27 526 women, respectively. Compared with women with normal AFI, those with isolated oligohydramnios had significantly higher rates of an infant with meconium aspiration syndrome (relative risk (RR), 2.83; 95% CI, 1.38-5.77), Cesarean delivery for fetal distress (RR, 2.16; 95% CI, 1.64-2.85) and admission to the neonatal intensive care unit (NICU) (RR, 1.71; 95% CI, 1.20-2.42). Patients with oligohydramnios and comorbidities were more likely to have an infant with low birth weight (RR, 2.35; 95% CI, 1.27-4.34). However, rates of 5-min Apgar score < 7 (RR, 1.85; 95% CI, 0.69-4.96), NICU admission (RR, 2.09; 95% CI, 0.80-5.45), meconium-stained amniotic fluid (RR, 1.32; 95% CI, 0.62-2.81) and Cesarean delivery for fetal distress (RR, 1.65; 95% CI, 0.81-3.36) were similar to those for women with normal AFI. Stillbirth rates were too low to analyze in the meta-analysis.

CONCLUSIONS

This review helps to delineate which adverse outcomes are increased with oligohydramnios in low-risk pregnancy (NICU admission, Cesarean delivery for fetal distress and meconium aspiration syndrome), but does not provide enough data to determine the optimal timing of delivery in such cases. Oligohydramnios in complicated pregnancy is associated with an increased risk of delivery of an infant with low birth weight, but this may be confounded by the comorbid condition. Therefore, in high-risk pregnancy, management should be dictated by the comorbid condition and not the presence of oligohydramnios. Copyright © 2016 ISUOG. Published by John Wiley & Sons Ltd.

Anxiolytic-like actions of fatty acids identified in human amniotic fluid

Eight fatty acids (C12–C18) were previously identified in human amniotic fluid, colostrum, and milk in similar proportions but different amounts. Amniotic fluid is well known to be the natural environment for development in mammals. Interestingly, amniotic fluid and an artificial mixture of fatty acids contained in amniotic fluid produce similar anxiolytic-like actions in Wistar rats. We explored whether the lowest amount of fatty acids contained in amniotic fluid with respect to colostrum and milk produces such anxiolytic-like effects. Although a trend toward a dose-response effect was observed, only an amount of fatty acids that was similar to amniotic fluid fully mimicked the effect of diazepam (2 mg/kg, i.p.) in the defensive burying test, an action devoid of effects on locomotor activity and motor coordination. Our results confirm that the amount of fatty acids contained in amniotic fluid is sufficient to produce anxiolytic-like effects, suggesting similar actions during intrauterine development.

Amniotic fluid water dynamics

Water arrives in the mammalian gestation from the maternal circulation across the placenta. It then circulates between the fetal water compartments, including the fetal body compartments, the placenta and the amniotic fluid. Amniotic fluid is created by the flow of fluid from the fetal lung and bladder. A major pathway for amniotic fluid resorption is fetal swallowing; however in many cases the amounts of fluid produced and absorbed do not balance. A second resorption pathway, the intramembranous pathway (across the amnion to the fetal circulation), has been proposed to explain the maintenance of normal amniotic fluid volume. Amniotic fluid volume is thus a function both of the amount of water transferred to the gestation across the placental membrane, and the flux of water across the amnion. Membrane water flux is a function of the water permeability of the membrane; available data suggests that the amnion is the structure limiting intramembranous water flow. In the placenta, the syncytiotrophoblast is likely to be responsible for limiting water flow across the placenta. In human tissues, placental trophoblast membrane permeability increases with gestational age, suggesting a mechanism for the increased water flow necessary in late gestation. Membrane water flow can be driven by both hydrostatic and osmotic forces. Changes in both osmotic/oncotic and hydrostatic forces in the placenta my alter maternal-fetal water flow. A normal amniotic fluid volume is critical for normal fetal growth and development. The study of amniotic fluid volume regulation may yield important insights into the mechanisms used by the fetus to maintain water homeostasis. Knowledge of these mechanisms may allow novel treatments for amniotic fluid volume abnormalities with resultant improvement in clinical outcome.

Paris heat wave and oligohydramnios

OBJECTIVE

The objective of this study was to determine the frequency of oligohydramnios in term pregnancies during the Paris heat wave of 2003 (August 4-14).

STUDY DESIGN

A comparison of this frequency to a historical control group examined during the same period in 2002.

RESULTS

The frequency of oligohydramnios in normal term pregnancies was 17.5% during the heat wave that affected Paris in August 2003.

CONCLUSION

This frequency was substantially higher than the rate of oligohydramnios in normal term pregnancies in August 2002 (4.4%).