Mirja A. Minger ^1,2* Grit Sommer ^3,4,5 Vera R. Mitter ^2,6 Livia A. Purtschert ⁷ Michael Von Wolff ² Alexandra S. Kohl Schwartz ^2,8*

• ¹ Department of General Surgery, Cantonal Hospital of Graubünden, Chur, Switzerland
• ² Department of Gynecology, Division of Gynecological Endocrinology and Reproductive Medicine, University Hospital of Bern, Bern, Bern, Switzerland
• ³ Department of Pediatric Endocrinology, Diabetology and Metabolism, University Children’s Hospital Bern, Bern, Bern, Switzerland
• ⁴ Department of Biomedical Research, Faculty of Medicine, University of Bern, Bern, Bern, Switzerland
• ⁵ Institute for Social and Preventive Medicine, Department of Preclinical Medicine, Faculty of Medicine, University of Bern, Bern, Bern, Switzerland
• ⁶ Division of Midwifery, Department of Health Professions, Bern University of Applied Sciences, Bern, Bern, Switzerland
• ⁷ Department of Pulmonology, Luzerner Kantonsspital, Lucerne, Switzerland
• ⁸ Department of Gynecology, Division of Reproductive Medicine and Gynecological Endocrinology, Luzerner Kantonsspital, Lucerne, Switzerland

Background: In recent studies, singletons conceived after in vitro fertilization (IVF) or intracytoplasmic sperm injection (ICSI) cycles had lower birth weight than spontaneously conceived singletons. The etiology of the impaired intrauterine growth is unclear, but insufficiency of placental function or possible epigenetic effects is discussed. Up to now, the growth of children born after unstimulated natural cycle ICSI (NC-ICSI) has never been studied. Material and Methods: We conducted a single-center, prospective cohort study (2010-2017) including children (n = 139) born after NC-ICSI or conventional gonadotropin stimulated ICSI (c-ICSI) treatment. Growth parameters up to 24 months were collected. Standard deviation scores based on growth references were calculated. Results: The median birth weight in NC-ICSI children was 3.4kg (0.1 standard deviation score (SDS)) compared to 3.3kg (-0.3 SDS) in c-ICSI children (p=0.61). Median length at birth was 50cm in both groups (NC-ICSI (-0.5 SDS), c-ICSI children (-0.8 SDS), p=0.48). At age 24 months, median weight in NC-ICSI children was 12.2kg (0.3 SDS) versus 12.2kg (0.2 SDS) in c-ICSI children (p=0.82) and median length 87.5cm (0.1 SDS) versus 88.0cm (0.4 SDS) (p=0.43).We found no difference in growth between children conceived after stimulated and unstimulated ICSI. Growth parameters of both treatment groups did not differ from Swiss national growth references. One of the main limitations of our study was the small sample size (N=139) and the high drop-out rate of 49% (68/139).