The findings of this study of a retrospective cohort of women with singleton deliveries who experienced pregnancies complicated or not with hyperemesis gravidarum revealed no significant impact of hyperemesis gravidarum on maternal and fetal outcomes in terms of fetal birthweight, 5-min APGAR scores, preterm birth, SGA, pregnancy-induced hypertensive disorder, placental abruption, stillbirth and GDM.
Similar to these findings, in a previous retrospective cohort study of fetal and maternal outcomes in pregnancies with or without hyperemesis from Turkey, no statistically significant differences were reported between pregnancies with or without hyperemesis in terms of rates of SGA birth, preterm birth, Apgar scores, fetal birth weight, gestational diabetes, pregnancy-induced hypertension, or fetal gender and type of delivery [8]. The authors of that study concluded that hyperemesis gravidarum was not associated with adverse pregnancy outcomes [8].
Likewise, in a Norwegian mother and infant cohort of 71,468 singleton pregnancies, no association of hyperemesis gravidarum was reported with low birthweight, preterm birth, delivering SGA infant and 5-min Apgar scores, regardless of the maternal weight gain (< 7 kilos or ≥ 7 kilos) [3].
The current study findings revealed similar risks for placental abruption and placental insufficiency disorders including gestational hypertension, pre-eclampsia and stillbirth in pregnancies complicated or not with hyperemesis gravidarum. This supports the data from a prospective cohort study of 2252 pregnant women, which indicated no association of hyperemesis gravidarum with placental insufficiency (gestational hypertension, pre-eclampsia, stillbirth, miscarriage), with poor neonatal outcomes (birth weight, SGA, low birth weight, Apgar score at 5 min, gestational age at delivery) and placental outcomes (placental weight, and placental weight to birth weight ratio) [10].
However, although the current study findings support the view that that hyperemesis gravidarum requiring hospitalization was not associated with an increased risk for preterm birth, low birth weight or SGA [3,8], it should be noted that there are conflicting data in literature on fetal outcomes and placental conditions after in-utero exposure to maternal hyperemesis gravidarum [2].
In a population-based retrospective Norwegian cohort study of 156,000 singleton pregnancies, hyperemetic pregnancies were reported to be associated with an increased risk of low birth weight, SGA, preterm delivery, 5-min Apgar scores <7 (relative risks of 3.0, 2.8, 1.5 and 5.0, respectively) compared to pregnancies without hyperemesis, but only for women gaining less than 7 kg during pregnancy [4]. The authors indicated that the adverse infant outcomes associated with hyperemesis were related to and mostly limited to poor maternal weight gain [4].
In a Swedish cohort study, hyperemesis gravidarum in the first trimester was reported to be associated with an increased risk of later occurring pre-eclampsia, and preterm delivery with pre-eclampsia, in addition to placental abruption and delivering an SGA infant [11].
Findings from a Dutch historical cohort study of 1.2 million singleton births revealed an association of hyperemesis gravidarum with an increased risk for preterm delivery but not for SGA or low birth weight [12]. An American cohort study of 520,000 live births reported that hyperemesis gravidarum was associated with a higher likelihood of delivering a low birthweight and SGA infant [6].
In a meta-analysis of 13 case-control studies, 10 cohort studies and one cross-sectional study on hyperemesis gravidarum and pregnancy outcomes, it was reported that hyperemesis gravidarum was associated with a 30% increase in risk for preterm birth and SGA, and a 40% increase in risk for low birthweight [13].
In fact, low maternal gestational weight gain, regardless of maternal hyperemesis status, has been considered to be associated with an increased risk of preterm birth, low birth weight and intrauterine growth retardation [14,15]. This emphasizes the associations between hyperemesis gravidarum and adverse pregnancy outcomes to be related to poor maternal weight gain rather than the direct effect of hyperemesis gravidarum [3,4,7], in addition to the greater risk for growth retardation and fetal anomalies in hyperemesis gravidarum cases with weight loss > 5% of the pre-pregnancy weight [7].
Given that weight loss was evident (<6.9 kg in74.1% and 7–14.9 kg in 13.3%) in 91.4% of the women with hyperemesis gravidarum in the current study cohort, the lack of association of hyperemesis gravidarum or concomitant weight loss with adverse pregnancy outcomes supports the view that with good antenatal care and management of women hospitalized with hyperemesis gravidarum, the risk of adverse pregnancy outcomes is likely to be diminished [3].
Nonetheless, whether or not hyperemesis gravidarum was associated with negative short-term consequences, the possibility of long-term consequences related to fetal undernutrition during first trimester has also been suggested, including an increased risk for cardiovascular disease, diabetes and schizophrenia in later life [3,16,17].
Although the exact etiology of hyperemesis gravidarum remains unknown, it is considered to be a multifactorial disease [2]. The characteristics of women with hyperemetic pregnancies in the current study cohort support the consideration of hyperemesis gravidarum as a pregnancy-related complication being more commonly observed among young, non-smoker and primiparous mothers [2,18,19].
While adverse pregnancy outcomes of hyperemesis gravidarum are conflicting and the current study findings revealed no association of the condition with an increased risk of fetal or maternal outcomes compared to the control pregnancies, it should be noted that hyperemesis gravidarum has been associated with a significant psychosocial burden in women together with an adverse impact on daily activities [20]. This seems notable given the reported lack of support from healthcare professionals and suboptimal management of women with hyperemesis gravidarum [20].