Is hyperemesis gravidarum associated with placental weight and the placental weight-to-birth weight ratio? A population-based Norwegian cohort study
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).
Section snippets
Materials and methods
This is a population-based cohort study. MBRN was founded in 1967 and is based on mandatory reporting of all births after 12th week of gestation. We included all singleton births of primiparous women, babies born between gestational week 23–44, where placental weight was reported between 100 and 2500 g, and birth weight of the child was between 500 and 6000 g, in total 212,653 births. We included primiparous women only as birth weight and placental weight may increase with parity [18].
Results
Altogether 1.2% of women were registered with HG (2589). Compared to women without HG, women with HG were more likely to be non-smokers. According to age and educational level, no differences were observed between the groups. Among women with HG, a larger proportion of women were of non-western descent compared to women without HG (Table 1). Mean placental weight was for slightly higher for male offspring compared to females.
In bivariate analysis, no difference was observed according to
Discussion
To the best of our knowledge, this is the first study on HG and placental weight and the PW/BW-ratio. Our main finding is that women with HG carrying a female offspring have significantly higher PW/BW-ratio compared to women without HG. These women have almost 20% increased risk of having a PW/BW-ratio in the top-ten percentile. Similarly, HG was inversely associated with having PW/BW-ratio below the 10th percentile compared to women without HG. This was also restricted to female offspring.
Acknowledgments
We would like to thank MBRN for providing us the data for this study. In addition, we would like to acknowledge the Norwegian Resource Center for Women's Health, Rikshospitalet, Oslo, Norway for the financial support for this study.
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