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Pregnancies with fetal major congenital heart defects (CHDs) had significantly higher rates of poor obstetric outcomes than those without defects, a decade-long Danish nationwide cohort study found.

Nearly 23% of pregnancies with fetal major CHDs exhibited adverse obstetric outcomes compared with 9% of those without them (adjusted OR 2.96, 95% CI 2.49-3.53), researchers led by Gitte Hedermann, MD, of Statens Serum Institut in Copenhagen, reported .

"Almost one in four women carrying a child with a major congenital heart defect develop placenta-related adverse obstetric outcomes," Hedermann emphasized to MedPage Today.

Although women carrying a child with transposition of the great arteries did not have significantly increased risk, all other subtypes of fetal major CHDs carried greater risk of adverse obstetric outcomes, including:

• Preeclampsia (aOR 1.83, 95% CI 1.33-2.51)
• Preterm birth at less than 37 weeks (aOR 3.84, 95% CI 3.15-4.71)
• Fetal growth restriction (aOR 3.25, 95% CI 2.42-4.38)

The authors pointed out that the fetal heart and placenta develop concurrently and "are hypothesized to share common regulatory pathways in early fetal life," which may impact long-term outcomes for the children, though much is still unknown about this relationship.

"Other studies have shown that children born with a major congenital heart defect have increased morbidity and mortality if they are born preterm or with a low birth weight," Hedermann said. "Unfortunately, our study also highlights that these complications are more prevalent for this group."

Jerrie Refuerzo, MD, a maternal-fetal medicine physician with UTHealth Houston who was not involved in the study, said that she's already on high alert for adverse obstetric outcomes in this population.

However, the new evidence "is going to change the frequency by which I see these patients, especially as they get closer to their due date," Refuerzo told MedPage Today. "[For] the majority of these adverse outcomes, the frequency typically increases as they get closer to 37, 38, 39 weeks' [gestation], and so seeing them more frequently in the third trimester will be my new strategy for making sure we can intervene early to improve those outcomes."

She noted that for most isolated congenital anomalies, women come into the pregnancy healthy with no medical conditions. Because of this, the focus of prenatal care is often the fetus more so than the mother.

"We have to remember that it's a package deal -- it's mom and baby," she said, noting that whatever is happening to the mom -- like hypertension or preeclampsia -- directly or indirectly impacts the baby as well.

Hedermann's study utilized the Danish Fetal Medicine Database, which includes data on nearly all pregnancies in Denmark. The country has free healthcare, and 95% of pregnant people opt to get ultrasonography scans in the first and second trimesters.

Among 534,170 pregnancies during the study period from June 1, 2008 to June 1, 2018, only 745 had isolated fetal major CHDs. Singleton pregnancies that resulted in a live-born child at 24 weeks' gestation or later and without chromosomal abnormalities were included; stillbirths were excluded because of incomplete data. Infants with major CHDs and postnatally-diagnosed, associated major extracardiac malformations were also excluded.

Genetic testing was performed on 42% of included pregnancies. Median maternal age was 29 for those with major CHDs and 30 for those without. The majority of mothers identified as white (91.4%).

For children with more than one major CHDs, only the most severe diagnosis was registered. The primary outcome was a composite of preeclampsia, preterm birth, fetal growth restriction, or placental abruption; secondary outcomes included each adverse obstetric event individually.

An additional 10 studies (five cohort and five case-control) were included in a meta-analysis, which revealed that univentricular heart, atrioventricular septal defect, and tetralogy of Fallot were associated with a higher risk of preterm birth and fetal growth restriction. Again, though, fetal transposition of the great arteries wasn't associated with these outcomes.

In terms of limitations, authors noted that the associations between major CHD subtypes and other factors were hampered by small numbers. The database also didn't have data on preexisting gestational diabetes, a risk factor for both major CHD and adverse obstetric outcomes, although Denmark has very low levels of this condition. Plus, the study only included live births.

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