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\title{Re: Risk of pre-eclampsia after gastric bypass: a matched cohort study}



\author[1]{Marleen van Gelder}%
\author[2]{Hubertina Scheepers}%
\author[3]{Luc Smits}%
\affil[1]{Radboudumc}%
\affil[2]{Maastricht UMC+}%
\affil[3]{Maastricht University}%


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  \date{May 20, 2024}


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BJOG Exchange

\textbf{Re: Risk of pre-eclampsia after gastric bypass: a matched cohort
study}

\emph{Marleen M.H.J. van Gelder,\textsuperscript{1} Hubertina C.J.
Scheepers,\textsuperscript{2} Luc J.M. Smits\textsuperscript{3}}

\textsuperscript{1} Department for Health Evidence, Radboud Institute
for Health Sciences, Radboud university medical center, P.O. Box 9101,
6500 HB Nijmegen, The Netherlands.

\textsuperscript{2} Department of Obstetrics and Gynaecology, Maastricht
University Medical Centre, P.O. Box 5800, 6202 AZ Maastricht, The
Netherlands.

\textsuperscript{3} Department of Epidemiology, CAPHRI Care and Public
Health Research Institute, Maastricht University, P.O. Box 616, 6200 MD
Maastricht, The Netherlands.

Corresponding author:

Dr. Marleen van Gelder, Department for Health Evidence (HP 133), Radboud
university medical center, P.O. Box 9101, 6500 HB Nijmegen, The
Netherlands. Tel: +31-24-3666126. Email:
Marleen.vanGelder@radboudumc.nl.

\emph{Sir} ,

We read with great interest the research article by Dr Johansson et
al.,\textsuperscript{1} in which Swedish nationwide healthcare data were
used to assess the association between gastric bypass before pregnancy
and the risk of pre-eclampsia. We applaud the authors for their careful
matching approach in the selection of the control groups to prevent
confounding. However, we feel that the conclusion that gastric bypass in
itself is effective in the prevention of pre-eclampsia may still be
considered premature.

Because of the higher risk of nutritional deficiencies due to
micronutrient malabsorption after bypass procedures, lifelong
micronutrient supplementation is started at hospital discharge after
bariatric surgery. This recommendation includes supplementation of,
among others, vitamin D (3000 International Units
D\textsubscript{3}daily from all sources) and calcium (1200-2400 mg
daily in divided doses, depending on the type of bariatric
procedure),\textsuperscript{2}both of which have shown to decrease the
risk of pre-eclampsia. In a meta-analysis of 27 randomized controlled
trials, vitamin D supplementation was found to lower the risk of
pre-eclampsia with almost two-thirds (odds ratio 0.37, 95\% confidence
interval 0.26-0.52).\textsuperscript{3} A reduced risk was also observed
after high-dose calcium supplementation ([?]1 g/day) in a meta-analysis of
13 trials (relative risk 0.45, 95\% confidence interval
0.31-0.65).\textsuperscript{4} Although vitamin D increases intestinal
calcium absorption, co-administration of vitamin D and calcium does not
seem to result in additional benefit.\textsuperscript{3} Several
biological pathways for protective effects of vitamin D and calcium on
the occurrence of pre-eclampsia have been proposed.\textsuperscript{3,4}

Johansson et al. used propensity score matching to adjust for multiple
potential confounders, including pre-surgery or early-pregnancy BMI,
pre-existing diabetes, maternal age, smoking status, educational level,
height, country of birth, delivery year, and history of
pre-eclampsia.\textsuperscript{1} However, micronutrient supplementation
was not taken into account in the analyses, whereas at least a
substantial part of the reduction in the risk of pre-eclampsia observed
after gastric bypass before pregnancy could be attributable to
supplementation of vitamin D and calcium. With the current study design,
it is challenging to distinguish between the effect of gastric bypass
itself and the effect of vitamin D and calcium supplementation that was
initiated directly after the procedure on the risk of pre-eclampsia, as
virtually all women with a history of gastric bypass will have used
supplements during pregnancy. Although all pregnant women are routinely
counselled on vitamin D and calcium supplementation, we know from
clinical practice that uptake of these recommendations is low.
Restricting the matched control groups to women who also used vitamin D
and calcium supplements with similar dosages during pregnancy may solve
this problem, but it is questionable whether reliable information on
supplement use is available from nationwide registries.

Disclosures of interests:

The authors have no conflicts of interest to report.

Contribution to authorship:

MvG conceived and drafted the letter. HS and LS contributed revisions
and significant intellectual content. All authors approved of the final
version for publication.

Funding:

MvG was supported by the Netherlands Organisation for Health Research
and Development {[}ZonMw; grant number 848018010{]}.

References:

\begin{enumerate}
\tightlist
\item
  Johansson K, Wikstr\selectlanguage{ngerman}öm AK, Söderling J, Näslund I, Ottoson K, Neovius
  M, et al. Risk of pre-eclampsia after gastric bypass: a matched cohort
  study. BJOG 2021; https://doi.org/10.1111/1471-0528.16871.
\item
  Mechanick JI, Apovian C, Brethauer S, Garvey WT, Joffe AM, Kim J, et
  al. Clinical practice guidelines for the perioperative nutrition,
  metabolic, and nonsurgical support of patients undergoing bariatric
  procedures -- 2019 update: Cosponsored by American Association of
  Clinical Endocrinologists/American College of Endocrinology, The
  Obesity Society, American Society for Metabolic and Bariatric Surgery,
  Obesity Medicine Association, and American Society of
  Anesthesiologists. Obesity 2020;28:O1-O58.
\item
  Fogacci S, Fogacci F, Banach M, Michos ED, Hernandez AV, Lip GYH, et
  al. Vitamin D supplementation and incident preeclampsia: a systematic
  review and meta-analysis of randomized clinical trials. Clin Nutr
  2020;39:1754-1752.
\item
  Hofmeyr GJ, Lawrie TA, Atallah ÁN, Torloni MR. Calcium supplementation
  during pregnancy for preventing hypertensive disorders and related
  problems. Cochrane Database Syst Rev 2018;10:CD001059.
\end{enumerate}

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