Is hyperemesis gravidarum associated with placental weight and the placental weight-to-birth weight ratio? A population-based Norwegian cohort study

Abstract

Introduction

Studies have suggested a link between placental weight, placental weight-to-birth weight ratio (PW/BW) and adult health. Hyperemesis gravidarum (HG) may also have implications for adult health. No studies on HG and placental characteristics have been identified. We therefore explored the relationship between HG, placental weight and the PW/BW-ratio in a population-based cohort.

Methods

Singleton births to primiparous women between 1999 and 2009 with data on HG, placental weight and birth weight in the Medical Birth Registry of Norway (MBRN) comprised the study base (n = 200,390). HG was defined through ICD-10 code 021.0, 021.1 and 021.9. Gender and gestational age specific percentile curves for placenta weight and PW/BW ratio were used to define those below the 10th and above the 90th percentile of both outcomes. Associations between HG and dichotomous outcomes were studied by multiple logistic regression. Multiple linear regression was applied to study placental weight as a continuous variable. Male and female offspring were analyzed separately.

Results

The prevalence of HG was 1.2%. Women with HG and female offspring had significantly higher risk of a PW/BW-ratio above the 90th percentile (OR = 1.17, 95% CI: 1.03–1.34). HG and PW/BW-ratio below the 10th percentile were inversely associated (OR = 0.70, 95% CI: 0.56–0.89). For male offspring no association was observed for HG and PW/BW-ratio below the 10th or above the 90th percentile.

Discussion/conclusions

We observed positive associations between HG and high PW/BW ratio limited to female offspring only. The high PW/BW-ratio suggests that there may be a possible link between HG and adult health.

Introduction

Hyperemesis gravidarum (HG) is characterized by intractable nausea and vomiting during pregnancy [1]. It affects 0.8–3.2% of pregnant women and causes maternal weight loss, dehydration and nutritional deficiencies [2], [3]. Children exposed to HG during intrauterine life are previously reported to have higher risk of reduced birth weight, but the differences described are minor and not consistent [2]. Previous research has shown that adverse exposure in utero might affect future health, although birth weight is within normal range [4], [5], [6]. Fetal growth depends, however, on a well-functioning placenta as well as a hospitable environment in utero. HG might threaten optimal growth conditions given limited nutritional supply for the mother and baby, and due to the possibility of HG increasing stress-levels and triggering fight-or-flight responses [7], [8]. Little is known of the relationship between placental functioning and HG.

Placental weight has been described to reflect placental functioning [5], [9] where weight in either end of the spectrum has been associated with adverse outcomes for the offspring [10], [11]. Placental weight relative to the child's birth weight (PW/BW ratio) has been introduced to represent a more nuanced measurement of placental efficiency as apposed birth weight and placental weight alone. A high PW/BW ratio might indicate a disproportional heavier placenta compared to the child's weight and has been associated with increased risk of cardiovascular disease and diabetes in later life [5], [12]. A recent Norwegian review reported an association between both high and low PW/BW ratio and fetal death [13]. A Swedish study on HG and placental dysfunction disorders, found the risk of preeclampsia to double and a three-fold increase in the risk of placental abruption among women with HG compared to women without HG [14]. Another study also reported a modest association between HG and preeclampsia [15]. Since placental functioning also is believed to influence the risk of neurodevelopmental disease in the offspring, it has received increasing attention over the last years [16], [17].

The association between HG and placental functioning is unclear and the research is limited. To the best of our knowledge, there are no studies on the association between HG and placental weight or HG and the PW/BW-ratio. Such studies might provide new knowledge on the long-term effects of HG, explaining why there is a need for a large prospective cohort study on this topic. The aim of this study was to explore associations between HG and placental weight and PW/BW ratio using data obtained from the Medical Birth Registry of Norway (MBRN).