A new study has shown that underweight and overweight women are at a significantly higher risk of experiencing recurrent miscarriages compared to those of average weight.
A research team led by the University of Southampton assessed the link between women’s lifestyle and risk of recurrent pregnancy loss, defined as women having two or more consecutive early miscarriages. The systematic review and meta-analysis study has been published in the journal Scientific Reports.
Miscarriage is the most common complication of early pregnancy, affecting between 15% and 20% of all pregnancies.
Recurrent pregnancy loss is a complex disease and although often attributed to numerous medical factors and lifestyle influences, the cause is deemed “unexplained” in around 50% of cases.
The results of this latest study found that there are higher occurrences of successive miscarriages in mothers who are underweight (having a Body Mass Index score of less than 18.5), overweight (having a BMI between 25 and 30) and obese (having a BMI above 30).
The study’s first author, Dr. Bonnie Ng, MRC Fellow in Clinical and Experimental Sciences at the University of Southampton, said, “Our study included 16 studies and showed that being underweight or overweight significantly increases the risk of two consecutive pregnancy losses. For those with BMI greater than 25 and 30, their risk of suffering a further miscarriage increases by 20% and 70% respectively.”
The research team also set out to assess the impact of factors such as smoking and consumption of alcohol and caffeine. However they were unable to establish conclusively whether these have any impact or not due to inconsistencies of the results from a small number of studies and heterogeneity in women taking part in them.
Co-author Dr. George Cherian, specialist trainee in obstetrics and gynecology at Princess Anne Hospital, Southampton, said, “While our study did not find any associations between recurrent pregnancy loss and lifestyle parameters such as smoking, alcohol and caffeine intake, further large-scale studies are required to clarify this.”
Whilst recognizing that more observational and clinical research is needed to establish the full extent of lifestyle choices, the authors conclude that weight is a risk factor that can be modified to reduce the risk.
“Our findings suggest that having an abnormal BMI exacerbates a woman’s risk of suffering from repeated miscarriages, and so clinicians really need to focus on helping women manage this risk factor’ concluded Ying Cheong, professor of reproductive medicine at the University of Southampton and senior author on the paper.
“We want every pregnancy to have a happy ending” . But unfortunately, it is estimated that as many as 26% of all pregnancies end in miscarriage and up to 10% of clinically recognized pregnancies . Quantifying the full burden of miscarriage is challenging because pregnancy loss rates are higher when pregnancies are clinically recognized . Moreover, spontaneous abortions mainly occur in the first trimester of normal pregnancy [2,3,4].
Definition of pregnancy loss
There are a variety of terms to outline the definition of spontaneous abortion. Therefore, there are some definitions:
Early pregnancy loss is described by several national organizations as a non-viable intrauterine pregnancy during the 1st trimester (up to 12+6 weeks from the last menstrual period) . Past terminology has included “miscarriage,” “blighted ovum,” and “missed abortion.” 
Early second-trimester pregnancy loss occurs after 13+0 and before 20+0 weeks of gestation [2,4,5,6]. The American College of Obstetricians and Gynecologists (ACOG) estimates that loss of a pregnancy that is less than 20 weeks gestation is the most common form of pregnancy loss . Approximately 20 percent of pregnant women have some bleeding before 20 weeks’ gestation, and one-half will end in spontaneous abortion. Up to 20 percent of pregnancies will end in miscarriage .
Stillbirth or fetal death is described as pregnancy loss that happens at 20 weeks gestation and later, or baby loss at a weight of 350 grams or greater, is referred to as a stillbirth or fetal death [5,7].
The term “abortion” has been recommended to be changed to “spontaneous pregnancy loss” because of acknowledging the emotional aspects of losing a pregnancy 
Risk factors and cause of pregnancy loss
It is found that almost 50 % of cases of spontaneous pregnancy loss are due to fetal chromosomal abnormalities [2,3,4,6]. In the majority of instances, it is too early to determine the exact cause of pregnancy loss . Several risk factors will increase the risk of pregnancy loss. Advanced maternal age is an important risk factor [2,4,5,6].
Women being at the age of 20 to 30 are at risk of 8.9 % of miscarriage in pregnancy of 20 weeks’ gestation and less, and up to 74.7 percent for women over 40 years old of age . Maternal comorbidities such as antiphospholipid antibody syndrome, thrombophilia, hypertension, diabetes type 1 and 2, celiac disease, thyroid disease, inherited thrombophilia, and systemic lupus erythematosus (SLE) also greatly impact pregnancy loss [2,4,5,7].
Some risk factors can lead to several complications such as pregnancy loss or fetal demise. The risk factors are maternal infections with Parvovirus B19, cytomegalovirus infection (CMV), human immunodeficiency virus (HIV), syphilis, malaria [4,5,7]. Other risk factors that negatively influence pregnancy outcomes are exposure to environmental contaminants such as arsenic, lead, and organic solvents; furthermore, cigarette smoking, large amounts of caffeine use, alcohol and substance use, and some medications [2,4,5,7].
Another important and prevalent health concern in obstetrics and gynecology is maternal weight that led to numerous issues during and after pregnancy. Maternal obesity is considered one of the most commonly occurring risk factors seen in obstetric practice . Overweight and obese pregnant women are at a strongly increased risk of miscarriage, whether they conceived after natural conception or assisted reproductive measures .
The risk of miscarriage and pregnancy loss before the first liveborn child is 25-37 % higher in obese women . New-born babies of obese mothers are at increased risk of stillbirth, congenital anomalies, prematurity, macrosomia, neonatal death, and are at an increased risk of developing obesity and metabolic disorders in childhood [8,9,10].
In addition to increased risks of pregnancy loss, they are at increased risk for hypertension, preeclampsia, gestational diabetes, thromboembolism, deep vein thrombosis (DVT), postpartum hemorrhage, and reduction in breastfeeding frequency since obesity is associated with reduced prolactin response to suckling [8,10,11].
Body mass index (BMI) is established as a person’s weight in kilograms divided by the square of height in meters . The normal BMI, as seen in Table 1, should be around 18.5-24.9.
Categories of body mass index
BMI – body mass index
|18.5 – 24.9||Normal or Healthy Weight|
|25.0 – 29.9||Overweight|
|30.0 and Above||Obese|
The Centers for Disease Control and Prevention (CDC) reported in 2016 that the prevalence of obesity in women before pregnancy ranged from 16.6% to 27% . The worldwide prevalence of obesity almost tripled between 1975-2016 . From 1999-2000 through 2017-2018, the prevalence of obesity and severe obesity increased among adults .
Almost a quarter of reproductive-age women in the United States are obese with a body mass index of 30 kg/m2 or greater . Obesity is more consistently and strongly associated with pregnancy loss than either diabetes type 1 or type 2 . A meta-analysis of 16 studies done in 2008 demonstrated that a body mass index (BMI) higher than 25 was strongly associated with a nearly 70 % increased odds of spontaneous pregnancy loss after spontaneous or assisted conception .
A Danish case-control study of 1644 obese women (BMI ≥30) and 3288 age-matched controls (BMI 19.0-24.9) showed that obese women had a higher incidence of first-trimester miscarriage [odds ratio (OR) 1.2, 95% confidence interval (CI) 1.01-1.46] and recurrent first-trimester miscarriage (OR 3.5, 95% CI 1.03-12.01) .
Since obesity and overweight among women are increased nowadays, our focus of this review is to evaluate the association between maternal obesity and the risk of pregnancy loss. When considering mechanisms that could influence early pregnancy loss among obese women, it is conceivable that obesity’s effects on the oocyte or embryo could affect the embryo’s potential for development; furthermore, obesity may negatively influence the endometrium, influencing the risk of miscarriage .
Since that, we aim to investigate the mechanism and pathophysiology implicated in pregnancy loss in women with a high body mass index. Our goal is to investigate the studies done before showing us the relationship between high body mass and pregnancy loss.
reference link :https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7847782/
More information: Ka Ying Bonnie Ng et al. Systematic review and meta-analysis of female lifestyle factors and risk of recurrent pregnancy loss, Scientific Reports (2021). DOI: 10.1038/s41598-021-86445-2