Miscarriage Risk Is Strongly Linked to the Mother’s Age and Pregnancy History

According to a study published today in The BMJ, the chance of miscarriage varies substantially with a woman’s age, has a strong recurrent pattern, and is elevated following various pregnancy problems.

According to the researchers, the data show that miscarriage and other pregnancy issues may have similar underlying causes, indicating that more research is needed.

Miscarriage is a common pregnancy result, although estimating the risk is difficult due to inconsistencies in documentation. Since 2008, Norway has been one of the few countries where miscarriage data has been gathered continuously.

So a group of researchers lead by Maria Magnus of the Norwegian Institute of Public Health set out to estimate the probability of miscarriage among Norwegian women and assess the relationship with age and previous pregnancies.

They identified all pregnancies in Norway between 2009 and 2013 using Norwegian health registers (medical birth registration, patient register, and induced abortion registry).

The risk of miscarriage was calculated based on the woman’s age and previous pregnancy history, including induced abortions.

More focused studies of these associations might lead to new insights regarding the shared underlying causes of pregnancy complications and miscarriage.

According to the researchers

During the research period, there were 421,201 pregnancies. The overall miscarriage rate was 12.8 percent after accounting for induced abortions. Miscarriage risk was lowest among women aged 25-29 (10%) and grew rapidly after age 30, peaking at 53 percent among women aged 45 and up.

There was also a high probability of miscarriage recurrence. The risk of another miscarriage was increased by half after one, doubled after two, and four times greater after three consecutive miscarriages.

An increased chance of miscarriage was also indicated by previous pregnancy problems. For instance, if the woman’s previous pregnancy resulted in a preterm delivery or a caesarean section, or if she developed diabetes while pregnant (gestational diabetes).

Pre-eclampsia (abnormally high blood pressure) in the prior pregnancy, on the other hand, was not linked to a higher risk of miscarriage. Women who were born little themselves had a higher chance of miscarriage.

This is an observational study, so it can’t prove the cause, and the researchers acknowledge certain limitations, including the chance that early miscarriages that didn’t result in contact with expert healthcare services were missed.

Nonetheless, the researchers claim that these findings provide more exact estimates of the risk of miscarriage as a function of a mother’s age and that the risk of miscarriage is associated to some previous pregnancy problems.

“More focused studies of these associations might lead to new insights regarding the shared underlying causes of pregnancy complications and miscarriage,” they conclude.

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