Morning sickness and the placenta
Date of Award
Edith Cowan University
Doctor of Philosophy
School of Medical and Health Sciences
Background: Nausea and vomiting in pregnancy (NVP) is considered one of the ultimate reproductive health dilemmas and often misunderstood both biologically and conceptually. This phenomenon occurs in approximately eighty percent of pregnancies worldwide and there are many theories relating to the cause of symptoms, however, no origin has been identified. Morning sickness will be discussed primarily within a physiological framework that focuses on maternal characteristics, placental structure, and related birth outcomes. Interestingly, vomiting in pregnancy appears to be unique to the human species, which from an evolutionary medical perspective is thought to be the result of human adaptation to varying internal and external environments. Some human adaptations or the consequential effects of these adaptations are not always viewed as favourable, from our twenty-first century medical point of view. Women with an absence of NVP symptoms in pregnancy are understudied and therefore, an essential and informative addition to this cohort.
Aims: The primary focus of this research project was to investigate NVP in relation to maternal characteristics, placental structure, and birth outcomes in singleton pregnancies. This study also included an important subset of expectant mothers with no reported NVP symptoms. Characteristics of morning sickness for expectant mothers with pregnancies resulting from ART and non-ART conception were examined. Psychosocial outcome variables and morning sickness status were compared using three specific measures from the maternal health questionnaire (MHQ) [Social Provision Scale (SPS), Pregnancy Distress Scale (PDQ) and the Perceived Stress Scale (PSS)], and the Edinburgh Postnatal Depression Scale (EPDS) from the maternal medical records. Data generated from the MHQ, gross placental morphology, maternal and natal medical records were examined to determine the associations between morning sickness, placental structure, and birth outcomes (e.g., low birth weight, placental weight, and birth weight to placental weight ratio). A unique addition to this study was the consideration of the placental microbiome as a potential contributing factor to differences in women with different NVP status.
Methods: To investigate NVP characteristics and examine the role of the human placenta and NVP status, 625 expectant mothers with singleton pregnancies were recruited from two major hospitals in Perth, Western Australia. Pregnancies were the result of natural and assisted conception and expectant mothers participated in a cross- sectional survey consisting of a MHQ, and gross placental examination using gross morphologic analysis. On completion of placental analyses, data from the maternal and natal medical records were collected and characteristics compared for women with differing nausea and vomiting status. The characteristics of NVP were identified through statistical analyses of the data, including significant medical, clinical, and psychosocial factors. Gross placental morphology measures and birth outcomes were compared according to NVP status.
Results: NVP was experienced by most expectant mothers in this cohort (79%) with 21% of women experiencing no NVP and 3% clinically diagnosed with hyperemesis gravidarum (HG). Nausea was the most prevalent symptom followed by food avoidance and women were more likely to report the frequency of these symptoms as continuous, while retching and vomiting were episodic in nature. Symptoms were self-rated as moderate to severe, and all risk factors were positively correlated with NVP. Women with HG recorded associated variables including increased symptom frequency and severity, medication use and a majority of the risk factors from the MHQ. The severity and frequency of symptoms were significantly associated with a number of maternal characteristics including age of menarche, increased maternal weight/obesity on first antenatal booking and admission for delivery of the baby.
Increased psychosocial measures noted for women with NVP were related to the frequency and severity of symptoms. This was consistent for women who experienced HG and had pregnancies resulting from ART. ART treatments were also associated with an increased frequency and severity of symptoms. Women experiencing NVP reported higher overall scores for the Pregnancy Distress Questionnaire and Perceived Stress Scale when compared to women who had no NVP, and evaluation of the Social Provision Scale identified women with NVP had lower self-rating scores for Nurturance and Attachment.
Women in this study delivered normal healthy babies, with normal BW/PWR and ponderal index ranges. Placental measures were similar for NVP status groups across this cohort and a majority fell within the 10th and 90th centiles for BW and placental weight. Evaluation of placental weight for women with clinically diagnosed HG in ART and non-ART pregnancies found that women who conceived naturally and experienced HG had an increased trimmed placental weight (grams). Women with HG who conceived using ART were more likely to have a lower placental weight.
This was the first study to explore the association between the placental amniochorionic microbiome and morning sickness status in women with singleton pregnancies. Significant differences in microbial diversity were noted between NVP status groups. Women with NVP had a higher species diversity and those in the No NVP group having a lower microbial diversity.
Clinical relevance: This comprehensive study has produced new and insightful information, highlighting the role of maternal characteristics and placental development in maternal health and birth outcomes. A detailed examination of NVP and the relationship between NVP symptoms, have highlighted the need for research that explores symptom frequency and severity rather than the presence or absence of symptoms alone. Examination of medical and clinical characteristics for women with and without NVP have provided new theoretical understanding and this current research provides evidence-based findings linking NVP and placental anatomy that are important for perinatal health. Future research examining the biological mechanisms and NVP symptom expression would be valuable. As part of reproductive health, ongoing research that promotes clinical understanding and the effective management of nausea and vomiting in pregnancy will decrease patient distress and foster practitioner confidence. Documentation of key concepts related to the physiology of nausea and vomiting in pregnancy can provide an understanding of the pathways that lead to NVP. Expectant mothers will be empowered by having access to updated information promoting maternal and natal health outcomes. Importantly, information should be provided to partners, family, friends, and caregivers to assist, nurture and support all expectant mothers.
Access to this thesis is embargoed until 21st May 2025.
Sartori, J. A. (2023). Morning sickness and the placenta. Edith Cowan University. https://doi.org/10.25958/fkxz-xp39