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Consequences of obesity in pregnancy

Obesity is a chronic condition whose incidence and prevalence has been increasing significantly worldwide. In addition to the well-known long-term consequences, pregnancy is another situation that deserves to be highlighted due to the impact that maternal excess weight can bring. A survey by the US National Institute of Health and Nutrition showed an increase in the prevalence of maternal obesity, going from 29.8% in 2001-2002 to approximately 39% between 2017 and 2018. Only 2 in 5 women begin pregnancy with a BMI in the normal range in the US.

Regarding obesity during pregnancy, a review was published last month in the New England Journal of Medicine (NEJM), one of the most respected medical journals in the world. We will address the possible consequences that obesity can bring to pregnancy, bringing what is essential to know about this clinical context of great relevance.

Read too: Management of obesity in pregnancy

Obesity versus preconception

Obesity, through disturbances of the pituitary-hypothalamus-ovarian axis, can lead to menstrual irregularity, with anovulatory cycles and subfertility. It is also related to higher rates of abortions and greater difficulty in assisted reproduction processes.

Maternal-fetal impact on pregnancy

Obesity leads to a condition of chronic inflammation and insulin resistance. Added to this, there is the influence of the additional resistance generated by hormones against placental regulators, such as placental GH and placental lactogen. Such factors are part of the pathophysiological mechanisms that explain most of the conditions associated with obesity during pregnancy.

  • Gestational Diabetes Mellitus (GDM)

Meta-analyses show a 3 to 4 times greater risk of GDM in obese pregnant women than in pregnant women with a normal BMI. The risk of developing diabetes is about 70% in approximately 20 years after pregnancy.

The risk of pre-eclampsia (PE) doubles for every 5 kg/m² increase in BMI. However, PE develops in only 10% of obese pregnant women.

There is an association between higher rates of anxiety and depression in obese pregnant women. It is postulated that perhaps alterations in the hypothalamic-pituitary-adrenal axis, as well as immune dysregulation, explain these facts.

Maternal obesity also correlates with a higher incidence of fetal malformations, especially neural tube defects and heart defects. Excess adiposity can even interfere with the diagnosis, since fetal ultrasound becomes more limited due to technical difficulties. Macrosomia and increased size for gestational age (above the 90th percentile) can also be a consequence of maternal overweight. Furthermore, there is a higher risk of fetal and neonatal death, with a 5 kg/m² increase in BMI increasing the relative risk of stillbirth by 1.28 (1.15 – 1.43; 95% CI).

Childbirth and postpartum conditions

Premature birth: the association is controversial, but recent meta-analyses show an increase of about 17% in the risk of preterm birth in obese pregnant women.

Childbirth and complications: the risk of shoulder dystocia can be 2 to 2.5 times higher in pregnant women with a BMI greater than 35. Furthermore, there is a greater chance of needing labor induction and the use of oxytocin. The increase in adipose tissue in the pelvis can lead to a narrowing of the birth canal, which, in association with a larger fetus, may explain why such complications are more frequent in this scenario.
Obesity in itself is not an indication for cesarean delivery, but the risk of evolution to cesarean delivery is twice that of normal BMI pregnant women. In addition, two meta-analyses showed a higher risk of postpartum maternal hemorrhage (OR 1.43), risk of wound and surgical site infection (OR 3.34) and thromboembolism, reaching a 4x greater risk in pregnant women with a BMI above 40 kg/m².

Breastfeeding: even in breastfeeding, obesity can have an impact. Obese puerperal women are less likely to be able to breastfeed their children. A recent meta-analysis showed that mothers with obesity have a 44% higher risk of not being able to breastfeed their children than mothers with a normal BMI.
Factors that can impact this scenario are a high level of progesterone, higher rates of depression and difficulties in latching on to the breast anatomy, for example.

Final message

Obesity can have serious consequences for pregnancy, from greater difficulty in conception, through greater chances of miscarriage and maternal-fetal morbidity, culminating in a greater risk of fetal death.
Therefore, it is essential to raise the awareness of health professionals about the need for its control, advising women on the unfavorable outcomes linked to the pregnancy-puerperal cycle and carrying out adequate clinical follow-up.

This content was co-authored with Luiz Fernando Fonseca Vieira:
Resident Doctor (R4) in Endocrinology (HCFMUSP) ⦁ Telemedicine at Hospital Israelita Albert Einstein (HIAE) ⦁ Medical Residency in Internal Medicine at the Faculty of Medicine of the University of São Paulo (FMUSP) ⦁ Graduation in Medicine at Universidade Estadual Paulista Júlio de Mesquita Filho (UNESP) – Botucatu School of Medicine ⦁ Instagram: @luiz_ffvieira

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