Objective
In a large, prospective Swedish national cohort, we investigated individual birth characteristics for women who had undergone bariatric surgery and their obstetric outcome and made comparisons with all other women during the same period.
Study Design
The cohort consisted of 494,692 women born 1973-1983 of which 681 women who had undergone bariatric surgery constituted the index group.
Results
The index women more often have parents with lower sociodemographic status and are more often born large for gestational age. The women surgically treated before their first child had a shorter gestational length, their children had lower birthweight, and were more often born small for gestational age compared with the children born to the reference mothers. Women whose child was born before their bariatric surgery more often had a cesarean section, and their children were more often large for gestational age.
Conclusion
Preconception bariatric surgery in obese women may be associated with improved obstetric outcomes.
Obesity has reached epidemic proportions globally, with at least 300 million adults clinically obese according to the World Health Organization. Obesity is a major contributor to the global burden of chronic disease and disability. An increasing number of women and female adolescents have obesity today both in the Western world and in developing countries.
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Obese women are more often afflicted with gestational hypertension and gestational diabetes. There is an increased risk of birth defects in the offspring of obese mothers, most pronounced for neural tube defects, congenital heart defects, and orofacial clefts. A number of threatening complications during pregnancy for both the mother and the infant occur more often among obese women.
Obesity is known to lessen quality of life, and in all likelihood has done so before it was recognized as a social and medical problem. Voluntary weight loss by dieting is effective in the short perspective, and is the mainstay of treatment, whether “self-administered” or under professional supervision. Long-term efficacy of dieting is disappointing, and the same, regrettably, holds true for pharmacologic treatment as an adjunct.
In the last few decades, effective treatment has become available by surgical means. Early surgical methods were flawed by side effects, and some later methods could indeed diminish these effects, at the price of not so successful weight loss. The most widely used method today, gastric bypass, seems to strike an attractive balance between good long-term weight loss and acceptable side effects. This balance, as well as the feasibility of this operation laparoscopically, has resulted in a rapidly growing number of patients undergoing gastric bypass. Among these are many fertile women, most centers report 80% of patients undergoing obesity surgery are female.
There are several studies that have evaluated obstetric outcome after bariatric surgery. Overall, it seems as if both pregnancy and delivery complications are reduced after surgery but the studies differ in design as well as how the control groups are chosen. Some studies compare outcome between women who underwent surgery with obese controls, others use control subjects stratified by body mass index (BMI).
Swedish population-based registers are prospectively collected and contain well-validated data. They therefore provide a unique opportunity to study sociodemographic background factors and reproductive pattern.
The objective of this study with a large prospective cohort from Swedish medical health registries was 2-fold. First, the individual birth characteristics for women who had undergone bariatric surgery were compared with all other women in the cohort during the study period. Second, the obstetric outcome was assessed among women delivering their first child after or before bariatric surgery compared with all other women during the same period, after suitable adjustments.
Materials and Methods
Women born between 1973 and 1983 were chosen as study cohort, because bariatric surgery commenced in the late 80s in Sweden in its modern form. The oldest women in our cohort would then have been in their late teens, and thus eligible for bariatric surgery. The limit to 1983 was chosen so as not to include too many women who had not yet given birth.
The index groups were thus women born between 1973 and 1983, having undergone surgery to attain weight loss, either before or after delivery of their first child. All women born in the same time span served as reference group.
Socioeconomic data for the parents to the studied women was recorded, as well as characteristics related to the women’s own birth in 1973-1983. We then collected socioeconomic data, as well as health related factors such as BMI, diabetes, hypertension/preeclampsia, and smoking prevalence at the time of the studied women’s own first pregnancy. Finally, obstetric outcome of the study cohorts first childbirth were recorded.
The Swedish Medical Birth Register (MBR) was established in 1973 and covers approximately 99% of all births. The register contains information on birth outcomes as well as certain maternal characteristics. Almost all pregnant women in Sweden regularly visit antenatal clinics, usually from the 6-9th week of gestation; from these records several data such as pregestational weight, BMI and smoking habits can be retrieved. The Total Population Register (TPR) contains information on births, deaths, marital status, as well as information on migrations, and country of origin for Swedish residents born abroad.
The National Patient Register (NPR) has been in use since 1964 and from 1987 and onward it covers all inpatient care in Sweden. The diagnoses in the NPR are based on the Swedish version of the World Health Organization international classification of diseases (ICD). ICD-8 was used until 1986, ICD-9 was used between 1987 and 1996, and ICD-10 from 1997 and onward. The Causes of Death Register records information on all deceased persons registered in Sweden at the time of death, and, by use of the Multi-Generation Register, it is possible to identify the fathers of the children registered in the MBR and the TPR. Information on the educational level of the women in the study population as well as their parents was retrieved by means of the Education Register and the Population and Housing Census 1970, respectively.
All women born in 1973-1983 according to the MBR and the TPR, who were alive and still living in Sweden at 13 years of age, served as the study population (n = 500,245). Women with missing values on birthweight and/or gestational length were excluded (n = 3360), as were those with extremely high or low birthweights relative to their length of gestation (2193 women). The final cohort therefore consisted of 494,692 women who were followed up until the end of year 2006. During the study period, 4.3% of the women emigrated and 0.38% were deceased. The 494,692 women were then individually linked to the maternal personal identification numbers for births occurring in the MBR before the year of 2006 (the first birth occurred in 1987). At the time of the study the women were 23-33 years old, with maximum maternal age thus 33 years. In the Swedish population, mean age at first childbearing is 29.8 years and a large proportion of our study population is still to experience their first pregnancy. A total of 189,819 mother-firstborn-offspring pairs were identified, of which 912 pairs were excluded because of missing values on the child’s birthweight and/or gestational length and an additional 40 because of the children having extremely high birthweights compared with the length of gestation. Thus, 188,867 mother-firstborn-offspring pairs were available for analysis.
Bariatric surgery was defined as women having had gastroplasty, gastric banding, or gastric bypass, whether performed with laparoscopic or open technique. These formed the vast majority of patients, singular cases were identified with other methods such as intragastric balloon or duodenal shunt with biliopancreatic diversion, none of these were included in the analysis as they were too few and there is also some uncertainty about the coding for these procedures. The information on the operated women was retrieved from the NPR. Information on socioeconomic and other background characteristics of both the studied women and their parents was retrieved from the registries previously mentioned. On the parents, we had information on their educational levels in 1985, their country of origin, as well as the mothers’ marital status, parity, and age at the time of giving birth (ie, 1973-83). For the women we had information on several birth-related variables such as birthweight, gestational length, instrumental delivery, cesarean section, as well as if the women were the result of a twin birth. Preterm birth was defined as less than 37 completed weeks of gestation, small for gestational age (SGA) was defined as a birthweight less than 2 standard deviations below the mean birthweight and large for gestational age (LGA) was defined as a birthweight more than 2 standard deviations according to Swedish external standards from 1996. Normal delivery was defined as a vaginal delivery without any instrumental assistance. Furthermore, we were able to retrieve information on the women’s educational levels and marital status at the time of giving birth. For the women who became mothers during the study period, we also had information on cohabitation status, BMI, and smoking habits during early pregnancy, as well as age when giving birth.
Statistical analyses
Women who had undergone surgery to attain weight loss were compared with all women born in the same time span by means of the χ 2 test and the t test.
The data were also modeled through Cox’s proportional hazards model to estimate the effect of bariatric surgery on the women’s subsequent likelihood of giving birth. The time-dimension was defined as age and subjects exited from risk when they gave birth to the first child, emigrated for the first time, died, or reached the end of follow-up, whichever took place first. Both crude and adjusted hazard ratios (HRs) and corresponding 95% confidence intervals (CIs) were calculated. Adjustments were made for parental socioeconomic characteristics. In addition to the χ 2 tests presented in Tables 1 and 2 , differences between the women who had undergone bariatric surgery and those who had not, were estimated by means of multiple logistic regression analysis, controlling for the background variables presented in Tables 3 and 4 , and the odds ratios (ORs) and corresponding CIs were calculated. By using this method, we were able to simultaneously account for the combined effect of the studied variables. However, as the differences between these analyses and the χ 2 tests presented in the tables are not substantial; we chose not to present the results of these additional analyses.
| Bariatric surgery | |||||
|---|---|---|---|---|---|
| No | Yes | ||||
| Variable | n | % | n | % | P value |
| Gestational length (mean/SD) | 39.7 | 1.8 | 39.7 | 1.9 | .812 |
| Birthweight (mean/SD) | 3429.7 | 520.8 | 3484.3 | 582.7 | .006 |
| Born preterm | |||||
| No | 472,216 | 95.6 | 643 | 94.4 | .138 |
| Yes | 21,795 | 4.4 | 38 | 5.6 | |
| Born SGA | |||||
| No | 475,398 | 96.2 | 653 | 95.9 | .638 |
| Yes | 18,613 | 3.8 | 28 | 4.1 | |
| Born LGA | |||||
| No | 482,150 | 97.6 | 653 | 95.9 | .004 |
| Yes | 11,861 | 2.4 | 28 | 4.1 | |
| Twin birth | |||||
| No | 485,677 | 98.3 | 669 | 98.2 | .879 |
| Yes | 8334 | 1.7 | 12 | 1.8 | |
| Normal delivery | |||||
| No | 150,825 | 30.5 | 189 | 28.4 | .238 |
| Yes | 343,202 | 69.5 | 476 | 71.6 | |
| Instrumental delivery | |||||
| No | 469,153 | 95.0 | 655 | 96.2 | .148 |
| Yes | 24,858 | 5.0 | 26 | 3.8 | |
| Cesarean section | |||||
| No | 447,202 | 90.5 | 614 | 90.2 | .746 |
| Yes | 46,809 | 9.5 | 67 | 9.8 | |
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