ArticlesDeliveries and children born after in-vitro fertilisation in Sweden 1982–95: a retrospective cohort study
Introduction
More than 20 years have passed since the first baby was born after in-vitro fertilisation.1 A 1995 world report showed that each year more than 40 000 babies are born worldwide after in-vitro fertilisation.2 In Sweden, the number of births after this treatment accounts for 1·6% of all neonates.
Perinatal outcome after in-vitro fertilisation has remained under scrutiny by the medical profession and the general public. Outcomes differ from those after spontaneous conception, mainly because of the high frequency of multiple pregnancies.3 Most countries report an incidence of multiple births of 20–30% after assisted conception, which leads to 30–40% of all in-vitro-fertilisation babies being born as a result of multiple pregnancies, compared with 2–3% in the general population.2 Treatment of infertility by assistedreproduction technology is thought to be an important contributing factor to the increase in multiple births seen in many developed countries in the past few decades.4 This increase has raised concerns, not only about the social consequences but also because multiple-birth babies are at higher risk of perinatal mortality and morbidity and of long-term sequelae (eg, cerebral palsy) than singletons.5
Studies have also shown that in-vitro-fertilisation singleton pregnancies have higher complication rates than those in the general population. In particular, the rate of preterm deliveries is higher and there is an increased risk of babies being small for gestational age.6, 7 Mothers who achieve a pregnancy after in-vitro fertilisation are generally older and have a lower parity than mothers who conceive their children naturally, which confers a higher risk of maternal and perinatal complications. One study has also shown that infertility contributes to increased obstetric risks.8
The introduction of new technologies has raised concerns that offspring may be at increased risk, especially of malformations. No evidence has yet shown that cryopreservation is an additional risk factor for perinatal outcome9, 10 but studies suggest an increased risk of chromosomal anomalies, mainly of the sex chromosomes, after intracytoplasmic sperm injection.11, 12 Since many perinatal outcomes—malformations and perinatal mortality—occur with a low frequency, a large study group is needed to investigate the risks with sufficient power. We aimed to assess the outcome of the complete Swedish in-vitro-fertilisation birth cohort from 1982 to 1995 compared with all births in Sweden during the same period, from data from existing registries on birth, malformation, cancer, and death.
Section snippets
Study group
The study group included all children born in Sweden after in-vitro fertilisation, from the first child born in 1982 to the last child born before April, 1995. Individual data on women after in-vitro fertilisation were, with permission from the Swedish Data Inspection Board, requested by the National Board of Health and Welfare from all 14 in-vitro-fertilisation clinics in Sweden.
In Sweden, every individual has a unique identification number that is widely used by health-care and social-service
Identified deliveries
4634 deliveries (in 4353 women) after in-vitro fertilisation were reported from the clinics, 4517 (97·5%) of which could be identified in the Swedish Medical Birth Registry. 77 deliveries had not been reported to this registry but were identified in the official birth registry of Statistics Sweden. Thus, only 40 (0·9%) deliveries of those reported from the clinics could not be identified as delivered. The number of deliveries reported from the clinics was checked against the cumulative annual
Discussion
In-vitro fertilisation in Sweden resulted in the birth of nearly 6000 children from the procedure's introduction in 1982 to 1995. Most of these children were born healthy. Our retrospective registry study of these babies has several unique features: it was a large controlled study; it was an investigation of all children born after in-vitro fertilisation in Sweden and not a sample; the various sources of data (reports from all in-vitro fertilisation centres, the Swedish Medical Birth Registry,
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