Table 3.

Hazard ratio (HR) with 95% confidence interval (CI) for maternal cardiovascular death by first and second sibling z-score by birth weight, the Medical Birth Registry of Norway, 1967 to 2002 on 158 772 sib pairs with z-score >=0 to <4. Estimates were adjusted for maternal age and year of birth of the first sibling, with follow-up until 2009.

Z-score by birth weight for sibling 1 and 2	Sibling pairs (n)	Maternal deaths per 1000	HR (95% CI)
Sibling 1: >2.5 and Sibling 2: >2.5	529	9.45	8.5 (3.5–20.7)
Sibling 1: >2.5 and Sibling 2: ≥0 to 2.5	2 422	4.12	3.4 (1.8–6.4)
Sibling 1: ≥0 to 2.5 and Sibling 2: >2.5	5 418	2.21	1.8 (0.99–3.2)
Sibling 1: ≥0 to 2.5 and Sibling 2: ≥0 to 2.5	150 403	1.41	1.0 (Reference)