This study demonstrates that bariatric surgery is effective at improving factors that may underlie fertility and pregnancy outcomes: body weight, type 2 diabetes, menstrual dysfunction, and PCOS. Although baseline numbers may be questioned in view of missing data, our results demonstrate improvements in the prevalence of each comorbidity, even after application of sensitivity analyses.
The meta-analyses have demonstrated that bariatric surgery improves maternal health during pregnancy (including reduction in rates of gestational diabetes [11–13] and hypertensive disorders [11, 13] as well as fetal benefits such as a reduction in rates of macrosomia [11–13]). Few studies have assessed the effect of bariatric surgery on menstrual disorders (including PCOS), but those available demonstrate excellent results with 70–80 % achieving normal menstruation postoperatively [14, 15] although sample sizes are small. Future research should include a prospective cohort design to investigate whether the improvements in the comorbidities we have demonstrated also translate to improved fertility.
The dramatic effect on weight is in keeping with data on the overall bariatric surgery population . A consensus view is that a reduction in body weight of 10 % is a realistic target that may help improve fertility . Our data show that bariatric surgery is a very effective means to achieve such a target (87.3 % of patients achieved ≥10 % weight loss).
Our data gives an intimation of the relative importance to stakeholders of the comorbidities that lead to a decision for bariatric surgery. Our data confirm that type 2 diabetes is an important trigger for bariatric surgery  as it was overrepresented in the NBSR compared to the HSE cohort. However, only 3.5 % of patients with a single comorbidity had diabetes, suggesting that it is not necessarily taken as an indication on its own. A similar comparison to national data for PCOS and menstrual dysfunction could not be made as data in the national HSE cohort were not available for PCOS and menstrual dysfunction.
Of those with a single comorbidity, PCOS was recorded as frequently as diabetes (3.8 %) but almost twice as many had a record of menstrual dysfunction (8 %). Overall, our data demonstrate that PCOS is seen in one in six women having bariatric surgery and menstrual dysfunction is seen in almost one third of women.
The potential effect of bariatric surgery to improve fertility, whether as the primary aim of surgery or otherwise, highlights the importance of good preconception care—which is often suboptimal. In one study, 40 % of women were not aware of the recommendation to avoid pregnancy in the first 12–18 months and 30 % did not use any contraception in the 12 months after operation . Adherence to these recommendations may be important to avoid poor neonatal outcomes from macronutrient or micronutrient deficiencies [19, 20].
In order to maximize the benefits of bariatric surgery on fertility and pregnancy outcomes, the potential complications of surgery must be identified and managed appropriately. A recent retrospective analysis suggested a possible increase in neonatal mortality in mothers who underwent bariatric surgery, but this did not control for comorbidities that are likely to be important confounders . Nevertheless, there may be an increased risk of preterm delivery  and small-for-gestational-age newborns [11–13] that may be related to the type of procedure: Biliopancreatic diversion is much more likely to be associated with small-for-gestational-age neonates , while laparoscopic-assisted gastric bypass does not appear to increase the rate of small neonates . Note that our data demonstrate that gastric bypass is the most common operation and that biliopancreatic diversion is rarely performed. Although included in the NBSR, intragastric balloon insertion may be considered a bariatric procedure rather than surgery per se. Our data showed that while these patients have similar demographics at baseline, the reductions in BMI were less (49.8 ± 18.1 to 45.7 ± 15.0 kg/m2) and improvements in the comorbidities were not seen. Indeed, the rates of different operations in female patients of childbearing age closely match those in the total NBSR cohort (Table 1). The similar rates for each operation raise the issue of whether this is appropriate or whether different operations should be offered to these women.
Open and timely access to bariatric surgery is important to optimize its benefits. Our data demonstrate that ethnic minorities are under-represented in the operated population, suggesting reduced access. This will require further investigation to explain possible cultural barriers and to prevent health inequalities in access to services.
The operated cohort was older than the eligible population of age-matched women. One interpretation for this is that there is a lead time from patients being eligible for surgery to having the operation. This delay is important as it falls around the key age for pregnancy success with a diminishing ovarian reserve. It has been demonstrated that before the age of 37, obesity has a significant negative impact on fertility, whereas in older women, this effect is outweighed by advancing age . Thus, weight loss to improve fertility should ideally occur before this age . That such a delay is happening may be due to delays in identification of eligible patients, delays in referral, and waiting lists for the operation itself. Clinicians should consider the benefits of operating earlier in young obese women, especially if fertility is a major concern.
The limitations of this study stem from limitations of the registry itself. Further information on preoperative childbearing history, parous state, and postoperative pregnancy would allow more direct conclusions to be drawn about the effects on fertility and pregnancy. Other data surrounding preconception care such as postoperative micronutrient supplementation or deficiency, contraceptive use, and hormonal supplementation are not recorded. It should also be noted that there is no site visit for the verification of the reported data. In the NBSR, the data is self-reported by each surgeon.
In summary, over half of all bariatric procedures are carried out on women of reproductive age. At least one in three of these women have menstrual dysfunction at baseline. Bariatric surgery improves factors that underlie fertility and pregnancy outcomes. A prospective study is required to demonstrate that this effect translates into a positive effect on pregnancy outcomes.