Table 2.

Description of sample set

	Number of women	Details
Extraction MBR	150	Sister pairs where both had undergone caesarean section at a gestational length of more than 286 days
Excluded directly	2	One deceased and one emigrated
Excluded after interview	54	One or both sisters refused to participate
Added	10	Additional sisters or cousins
Total	104
Blood samples collected	83
Blood samples analyzed, Affymetrix	39	These women were included in the genetic analysis (NPL)
Blood samples analyzed, re-sequencing	68	These women were included in the re-sequencing of OXT and OXTR