1 New Jessop Wing, Obstetrics and Gynaecology, University of Sheffield, Sheffield S10 2SF and 2 Department of Obstetrics and Gynaeology, Solihull Hospital, Birmingham Heartlands and Solihull Hospitals NHS Trust, Solihull, West Midlands B91 2JL, UK
3 To whom correspondence should be addressed. e-mail: h.lashen{at}sheffield.ac.uk
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Abstract |
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Key words: obesity/miscarriage/recurrent miscarriage
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Introduction |
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Materials and methods |
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Obese women (BMI >30 kg/m2) and an age-matched control group with normal BMI (1924.9 kg/m2) were included in the study, based on the WHO criteria. For every obese woman, two age-matched normal weight (BMI 1924.9) controls were selected at random from the next database entry.
The two groups were compared with regard to their previous history of early (612 weeks gestation), late (1224 weeks gestation) and recurrent early (more than three) miscarriages using binary logistic regression analysis.
The prevalence of pre-pregnancy diabetes mellitus and gestational diabetes based on impaired oral glucose tolerance test (post prandial glucose of >7.5 mmol/l) were also compared between the two groups. Statistical analysis was carried out using Minitab for Windows, release 13.32 (Minitab Inc., PA, USA). The data are presented as mean or odds ratios (ORs) with the relevant 95% confidence intervals (CIs). A P-value <0.05 was considered significant.
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Results |
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The prevalence of diabetes mellitus in the two groups was very low, as only four patients in the obese group (0.2%) and none in the NWC group had pre-pregnancy diabetes. The prevalence of gestational diabetes was significantly higher among the obese patients (4.5%; 95% CI 3.55.5) compared with the NWC group (0.4%; 95% CI 0.20.6). This difference was statistically significant (OR 13.05; 95% CI 7.0724.07). P <0.001.
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Discussion |
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The risk of miscarriage after the detection of a fetal heart on ultrasound scan is reduced to 5%, except in patients who have had recurrent miscarriages (van Leeuwen et al., 1993).
Many factors have been described to increase the risk of spontaneous miscarriage; however, obesity was not found to be a risk factor by Risch et al. (1990). Recent evidence indicated that obese women undergoing infertility treatment were at increased risk of spontaneous miscarriage (Hamilton-Fairley et al., 1992
; Wang et al., 2000
). However, this point has also been controversial (Lashen et al., 1999
; Roth et al., 2003
).
In this study, we compared the incidence of early, late and recurrent miscarriage between a group of obese women and a randomly selected group of age-matched NWC. This is the first study of its kind, nested casecontrol, to assess such relationship in the general population according to the timing of miscarriage, i.e. early or late. Furthermore, this is also the first study to examine the prevalence of recurrent miscarriage among obese women in comparison with NWC. The exact reason for the obesity-related increased risk of miscarriage is not known. The possibility of oocyte abnormality was refuted by a recent study of obese women receiving oocyte donation who experienced a higher rate of spontaneous miscarriage compared with normal weight peers (Bellver et al., 2003). The prevalence of overweight and obesity among PCOS patients is
50% (Pasquali and Casimirri, 1993
). Therefore, it is unlikely that the increased risk of miscarriage among obese patients in this study population can solely be attributed to PCOS, owing to the low prevalence of PCOS in this general population with mostly spontaneous miscarriage. Furthermore, evidence has been reported that obesity is an independent risk factor for miscarriage (Fedorcsak et al., 2000
). Furthermore, Wang et al. (2001)
suggested that spontaneous abortion reported in women with PCOS may be due to their high prevalence of obesity.
A four-fold increase in the risk of spontaneous miscarriage was reported in diabetic pregnant women with poor glycaemic control in early pregnancy (Temple et al., 2002). However, in our study population the prevalence of pre-pregnancy diabetes was very low, precluding further assessment of this point. Notably, a higher incidence of gestational diabetes was observed in the obese group, which reflects an unphysiological insulin resistance that may play a role in the reported increased miscarriage risk. One could argue that type II and gestational diabetes are one condition differing in the time of detection, and that the worse the insulin resistance at the time of conception and in early pregnancy the higher the risk of miscarriage. This hypothesis can not be addressed in the context of this study, and perhaps a prospective cohort study is better suited to address this issue.
Endometrial receptivity is yet another plausible explanation for early miscarriage; however, evidence is lacking to rule out the oocyte as a potential cause. An unfavourable intrauterine milieu associated with obesity is an alternative explanation for the increased prevalence of miscarriage. However, the fact that all these patients had a successful pregnancy suggests a non-recurring cause for the miscarriage, pointing again to the oocyte quality issue. The retrospective nature of this study and the lack of some information regarding the patients who miscarried but who were not included in the database preclude identification of the cause for the increased risk of miscarriage in the obese population. Furthermore, some may argue that obesity can confer a protective effect in some obese patients, hence their successful pregnancy on this occasion. The weight of evidence so far does not support this hypothesis, and a specially designed cohort study is better suited to address it. This nonetheless, does not reduce the value of this study in identifying a link between obesity and early and recurrent miscarriages. A more precise cause is a prime subject for future research, which is justifiable in view of our and other researchers findings.
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References |
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Submitted on October 8, 2003; accepted on March 29, 2004.