The group looked at 60,650 singletons in a common Nordic database from ART registers in Denmark, Finland, Norway and Sweden and compared these to a control group of 360,022 naturally conceived (NC) singletons. In both groups 0.4 % of singletons were stillborn, with a definition of stillbirth as a dead child after 22 weeks of gestation. After having been matched with the control group regarding mother's parity and year of birth, the overall risk of stillbirth was found to be marginally higher (1.1 fold) in ART children after adjusting for factors such as maternal age and the child's sex.
"Although the difference in risk of stillbirth is significant between the two groups and the risk is marginally higher with an overrepresentation of 8 per 1,000 pregnancies for singleton ART pregnancies, the overall risk of stillbirth is still low," said Anna-Karina Aaris Henningsen, leading author of the study from Righospitalet University Hospital of Copenhagen. "This means that the individual woman need not be concerned about the risk of stillbirth during pregnancy."
When analysing the stillbirth risk before and after term, no difference was found after 40 weeks of gestation between ART children and their naturally conceived peers. This was also the case when comparing the two cohorts after 37 weeks of gestation. However, until gestational week 40, the group found a 1.2 fold higher risk of stillbirth for ART singletons.
"We believe the difference in risk of stillbirth between ART and NC children seems to occur before 37 weeks of gestation," said Dr. Aaris Henningsen. "It is likely, that some of the difference in risk of stillbirth is related to parental factors in the subfertile mother or father."
When the researchers assessed the risk of total perinatal death (risk of stillbirth and risk of perinatal death until one year of age), children born after ART showed a 1.4 fold increased risk compared to naturally conceived babies. This remained 1.2 fold higher after adjusting for confounding factors and can probably be partly explained by the higher risk of preterm birth among ART children.
"Very few European, non-Nordic, studies exist on stillbirth rates and are mostly based on small numbers," explained Dr. Aaris Henningsen. "Our results come from the largest database on ART children worldwide. The MART group is currently looking at multiple neonatal outcomes including the risk of perinatal death in both singletons and twins and is hoping to have additional data in the near future."
In 2006, the European IVF Monitoring Group (EIM), a working group of ESHRE decided to assess the possibility of using the Nordic ART registers to pool outcome data for infant and maternal health after ART. The Committee on Nordic ART and Safety (CoNARTaS) was established in order to provide a continuous and large scale Nordic monitoring system that reports on safety and quality aspects of ART. The Nordic ART database contains data on all ART pregnancies, deliveries and children born after IVF, Intracytoplasmic Sperm Injection (ICSI) and frozen embryo transfer (FET) in Denmark, Finland, Norway and Sweden.
Abstract no: O-300 Wednesday 6 July 2011, 14.30 hrs CEST (Room K1+K2)
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The figures in the release have been updated since the abstract was submitted to the conference.
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