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Asthma is a chronic reversible obstructive airway disease, which is common among children and leads to respiratory impairment. Studies showed that asthma is more common among children born after in vitro fertilization (IVF) than among spontaneously conceived children. However, it is unknown which component of the IVF procedure contributes to this putative link. Therefore, the aim of this prospective follow-up study was to differentiate the possible effect of ovarian hyperstimulation from that of the in vitro culture procedure on asthma and rhinitis in 9-year-old children conceived with IVF. The study comprised three groups of singletons: (I) conceived with ovarian hyperstimulation-IVF (COH-IVF, n = 95); (II) conceived with modified natural cycle-IVF (MNC-IVF, n = 48); and (III) naturally conceived to subfertile couples (Sub-NC, n = 68). Parents filled out the validated Dutch version of the asthma questionnaire of the International Study of Asthma and Allergies. Asthma prevalence in the groups did not differ: COH-IVF n = 8 (8%); MNC-IVF n = 0 (0%); and Sub-NC n = 4 (6%). Adjustment for confounders did not alter the results.Conclusion: Neither ovarian hyperstimulation nor the in vitro culture procedure was associated with asthma and rhinitis at 9 years. IVF children had a similar prevalence of asthma compared with children conceived naturally by subfertile couples.Trial registration: ISRCTN76355836 What is Known: • An increased risk for asthma has been observed in children born after in vitro fertilization at preschool and school age. • The association between IVF and asthma may be partly explained by parental subfertility. What is New: • IVF children do not have a higher prevalence of asthma than children of subfertile couples conceived naturally. • Ovarian hyperstimulation used in IVF is not associated with asthma in 9-year-old children of subfertile couples.

Singletons born after IVF are at risk of adverse pregnancy outcome, the cause of which is unknown. The present study investigated the influence of ovarian stimulation and IVF laboratory procedure on birthweight. Birthweight of singleton pregnancies resulting from IVF treatment with (n=161) and without ovarian stimulation (using a modified natural cycle (MNC) protocol; n=158), and spontaneous conceptions in subfertile patients (n=132) were compared. Mean+/-SD birthweight of singletons after conventional IVF with ovarian stimulation, MNC-IVF and natural conception were 3271+/-655, 3472+/-548 and 3527+/-582 g (P=0.001). After adjustment for biological and social confounders, the difference in birthweight between conventional IVF and MNC-IVF was reduced to 88 g and the differences between conventional IVF and MNC-IVF versus spontaneous conceptions to 123 and 23 g, respectively. The results lead to three conclusions. First, a major part of the crude differences in birthweight between the three groups is related to patient and pregnancy characteristics. Second, the IVF laboratory procedure has no influence on birthweight. Third, although a trend towards lower birthweight after ovarian stimulation was found, an adverse effect of ovarian stimulation on birthweight was not substantiated., (2010 Reproductive Healthcare Ltd. Published by Elsevier Ltd. All rights reserved.)