If obesity is a risk factor for preeclampsia, does that mean losing weight can help prevent it?
First of all, obesity is a risk factor for preeclampsia, but that does not necessarily mean it is a cause. There are some underlying conditions that can make it difficult to lose weight and also are risk factors for preeclampsia. It may not be the weight itself that is the problem, but the underlying thyroid disorder, insulin resistance, PCOS, etc.
Second, weight is just one factor in a long list of risk factors. Preeclampsia can happen to thin women, too. When we divide women based on weight (underweight, normal weight, overweight, obese) and see who gets preeclampsia, there are cases in all four groups. There will be slightly more in the overweight and obese groups compared to the normal and underweight groups, which is why it is counted as a risk factor. But preeclampsia can happen to women of any weight if they have other risk factors in play.
Now that we have that background, we can look at whether losing weight before pregnancy lowers risk. I pulled out four recent studies of decent quality on the topic.
One, looking specifically at IVF, first eliminated women with PCOS. It found that losing weight between pregnancies showed a lower risk of gestational hypertension but not preeclampsia (source).
The second study found that there was a small decrease in risk with losing weight, but the bigger finding was that gaining weight between pregnancies increased risk (source).
The third is probably the best quality because it had over a million subjects. It found that losing weight did not decrease risk, but gaining weight increased risk (source).
And the final one also found that losing weight did not decrease risk, but gaining weight increased risk (source).
Now, I want to be clear. You DID NOT cause preeclampsia by gaining weight between pregnancies. As I outlined above, there are some underlying conditions that cause weight gain and also raise the risk of preeclampsia. Pregnancy can trigger or unmask conditions we did not realize we had before. It is not unusual for a woman to have new symptoms or get a new diagnosis during or soon after a pregnancy. We are not putting blame on anyone for gaining too much weight. Also, if you have gained weight and are considering another pregnancy, an increase in risk does not mean you are doomed. You could still have an uncomplicated pregnancy.
We do encourage healthy lifestyle choices where possible. There are health benefits to losing weight, and your doctor may recommend it to help with certain other conditions. Maintaining a healthy weight to the best of your ability, eating plenty of vegetables and fruits, exercise, drinking water, etc, are all wonderful. Managing any health concerns like diabetes, thyroid imbalance, chronic hypertension, etc, is important. Being as healthy as possible may not prevent preeclampsia, but it can make recovery easier.