A case-control study of the interaction of fetal heart rate abnormalities, fetal growth restriction, meconium in the amniotic fluid and tachysystole, in relation to the outcome of labour

Increased risk of preterm birth due to heat exposure during pregnancy: Exploring the mechanism of fetal physiology

BACKGROUND

Heat exposure during pregnancy can increase the risk of preterm birth (PTB) through a range of potential mechanisms including pregnancy complications, hormone secretion and infections. However, current research mainly focuses on the effect of heat exposure on pathophysiological pathways of pregnant women, but ignore that maternal heat exposure can also cause physiological changes to the fetus, which will affect the risk of PTB.

OBJECTIVE

In this study, we aimed to explore the mediating role of fetal heart rate (FHR) in the relationship between maternal heat exposure and PTB incidence.

METHODS

We assigned heat exposure to a multi-center birth cohort in China during 2015-2018, which included all 162,407 singleton live births with several times FHR measurements during the second and third trimesters. We examined the associations between heat exposure, FHR and PTB in the entire pregnancy, each trimester and the last gestational month. The inverse odds ratio-weighted approach applied to the Cox regression was used to identify the mediation effect of heat exposure on PTB and its clinical subtypes via FHR.

FINDINGS

Exposure to heat significantly increased the risk of PTB during the third trimester and the entire pregnancy, hazard ratios and 95 % CIs were 1.266 (1.161, 1.379) and 1.328 (1.218, 1.447). Heat exposure during the third trimester and entire pregnancy increased FHR in the third trimester by 0.24 bpm and 0.14 bpm. The proportion of heat exposure mediated by FHR elevation on PTB and its subtype ranged from 3.68 % to 24.06 %, with the significant mediation effect found for both medically indicated PTB and spontaneous PTB.

CONCLUSIONS

This study suggests that heat exposure during pregnancy has an important impact on fetal health, and FHR, as a surrogate marker of fetal physiology, may mediate the increased risk of PTB caused by extreme heat. Monitoring and managing physiological changes in the fetus would constitute a promising avenue to reduce adverse birth outcomes associated with maternal heat exposure.

Does intrapartum epidural analgesia influence rate of emergency delivery for fetal compromise?

Linked articles: This Editorial comments on Damhuis et al. and Tabernée Heijtmeijer et al.

Risk factors for a serious adverse outcome in neonates: a retrospective cohort study of vaginal births

OBJECTIVE

To investigate the hypothesis that risk factors in addition to an abnormal fetal heart rate pattern (aFHRp) are independently associated with adverse neonatal outcomes of labour.

DESIGN

Observational prospective cohort study.

SETTING

17 UK maternity units.

SAMPLE

585 291 pregnancies between 1988 and 2000 inclusive.

METHODS

Adjusted odds ratios (OR) with 95% confidence intervals (95% CI) were estimated from multivariable logistic regression.

MAIN OUTCOME MEASURES

Adverse neonatal outcome at term (5-minute Apgar score <7, and a composite measure comprising 5-minute Apgar score <7, resuscitation by intubation and/or perinatal death).

RESULTS

Analysis was based on 302 137 vaginal births at 37-42 weeks inclusive. We found a higher odds of Apgar score at 5 minutes <7 with suspected fetal growth restriction (OR 1.34, 95% CI 1.16-1.53), induction of labour (OR 1.41, 95% CI 1.25-1.58), nulliparity (OR 1.48, 95% CI 1.34-1.63), booking body mass index ≥30 (OR 1.18, 95% CI 1.02-1.37), maternal age <25 (OR 1.23, 95% CI 1.10-1.39), black ethnicity (OR 1.21, 95% CI 1.03-1.43), early-term birth at 37-38 weeks (OR 1.13, 95% CI 1.02-1.25), late-term birth at 41-42 weeks (OR 1.14, 95% CI 1.01-1.28), use of oxytocin (OR 1.27, 95% CI 1.14-1.41), maternal pyrexia (OR 1.87, 95% CI 1.46-2.40), aFHRp and presence of meconium (aFHRp without meconium: OR 2.40, 95% CI 2.15-2.69; meconium without aFHRp: OR 2.20, 195% CI.94-2.49; both aFHRp and meconium: OR 4.26, 95% CI 3.74-4.87). The results were similar when the composite adverse outcome was considered.

CONCLUSIONS

A range of risk factors, including suspicion of fetal growth restriction, maternal pyrexia and presence of meconium, are implicated in poor birth outcomes in addition to aFHRp. Interpretation of the fetal heart rate pattern alone is insufficient as a basis for decisions about escalation and intervention.

The association between undetected small-for-gestational age and abnormal admission cardiotocography: A registry-based study

OBJECTIVE

To assess the association between undetected small-for-gestational age (SGA) fetuses and abnormal admission cardiotocography (admCTG) in a low-risk population.

DESIGN

An observational study.

SETTING

Four hospitals in Stockholm-Gotland, Sweden.

SAMPLE

A cohort of 127 461 deliveries between 1 February 2012 and 15 June 2020.

METHODS

This cohort was linked to the Swedish Neonatal Quality Register. Pregnancies were designated as high or low risk at the time of admission to the labour ward according to pre-defined risk measures. SGA was defined as a birthweight at or below the tenth centile and at or below the third centile for gestational age.

MAIN OUTCOME MEASURES

The main outcome was the proportion of undetected SGA by admCTG (normal or abnormal). The secondary outcome was a composite severe adverse neonatal outcome for fetuses born less than 6 hours after admission (Apgar score <4 at 5 minutes, hypoxic-ischaemic encephalopathy grade of 2-3, neonatal seizures and neonatal death).

RESULTS

The rate of abnormal admCTG was 4.9%. The proportion of SGA at or below the tenth centile was higher in the abnormal admCTG group than in the normal admCTG group, 18.6% versus 9.7% (odds ratio 2.1, 95% CI 1.9-2.3). Abnormal admCTG and SGA (≤10th) was associated with a more than 20-fold increased risk of an adverse outcome compared with normal admCTG and non-SGA (adjusted odds ratio 23.7, 95% CI 9.8-57.3). The latter had a risk of 1/2000 of an adverse outcome.

CONCLUSIONS

In this low-risk population, undetected SGA fetuses were more prone to having abnormal admCTG and had a substantially higher risk of severe adverse neonatal outcomes.