The National Women's Health Study: assembly and description of a population-based reproductive cohort

BMC Public Health

Table 3 Comparison with population birth data of reported births in Stages 1 and 2¹ of the National Women's Health Study occurring since 1980²

REGISTERED STILLBIRTH³
		No. stillbirths³	Total livebirths & stillbirths³	SRSR⁴ (95% CI)
Stage 1	1980–2002	102	18,740	115	(94 – 139)
Stage 2	1980–2002	59	12,061	102	(79 – 132)
MULTIPLE (REGISTERED) DELIVERY ⁵
		No. multiple deliveries⁵	Total deliveries⁵	SMDR⁴ (95% CI)
Stage 1	1980–2002	264	18,391	111	(99 – 126)
Stage 2	1980–2002	169	11,887	108	(93 – 126)
AVERAGE MATERNAL AGE AT FIRST ⁶ (LIVE)BIRTH (years)
		No. first⁶ livebirths	Mean (SD) age⁷	England & Wales⁸ Mean age
Stage 1	Year of delivery
	1980–84	1,724	25.2 (4.12)	25.5
	1985–89	1,916	25.9 (4.56)	26.4
	1990–94	2,058	27.1 (4.85)	27.8
	1995–99	2,026	28.6 (5.01)	29.0
	2000–02	699	29.4 (5.06)	29.6
Stage 2	1980–84	1,032	25.5 (4.02)	25.5
	1985–89	1,182	26.0 (4.45)	26.4
	1990–94	1,325	27.3 (4.78)	27.8
	1995–99	1,432	28.8 (4.81)	29.0
	2000–02	540	29.7 (4.89)	29.6

¹ Stage 2 data are a subset of Stage 1 data (see methods). ² Pregnancies with missing maternal age have been excluded from this analysis. ³ Registered stillbirths 1980–2002, defined as fetal death at ≥ 28 weeks prior to 1992, or at ≥24 weeks thereafter. 41 (40%) of stillbirths had no gestational age, but were described as stillbirths by the mother. Unit of analysis is a baby; multiple births counted as many times as there are babies. Denominator contains all reported livebirths and registered stillbirths 1980–2002. ⁴ Standardised Registered Stillbirth Ratio (SRSR) and Standardised registered Multiple Delivery Ratio (SMDR). Standardised for maternal age (5-year intervals) and single year of birth using data for England and Wales 1980–2002. ⁵ Unit of analysis is a delivery (pregnancy) containing one or more registered live or stillbirth; multiple pregnancies counted once only. Multiple pregnancies containing only one registered birth (with another non-registrable outcome, such as miscarriage) considered as singleton in this analysis. ⁶ First registered birth, if live. ⁷ NWHS data relates to livebirths both within and outside marriage ⁸ Livebirths within marriage only

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