Table 1.
Prenatal/Perinatal Factors and Risk of MS in the NHS and NHS-II Cohorts
| Variable | No. Participants | No. Casesa (prevalent and incidentb) | Multivariate-adjustedc: Incident and Prevalent Cases RR(95% CI) | Multivariate-adjusted c: Incident cases only RR(95% CI) |
|---|---|---|---|---|
| Birthweight (lb) | ||||
| <5.5 | 15,243 | 61 | 1.22 (0.93–1.60) | 1.29 (0.96–1.72) |
| 5.5–8.4d | 126,881 | 444 | 1.0 | 1.0 |
| 8.5–9.9 | 19,115 | 69 | 1.03 (0.75–1.41) | 1.13 (0.86–1.49) |
| 10+ | 2856 | 10 | 1.32 (0.67–2.59) | 1.08 (0.51–2.28) |
| P for trend | 0.41 | 0.43 | ||
| Season of birth | ||||
| Spring | 58,030 | 178 | 1.13 (0.88–1.46) | 1.11 (0.83–1.48) |
| Summer | 61,393 | 182 | 1.05 (0.70–1.59) | 1.04 (0.65–1.68) |
| Fall | 61,392 | 179 | 0.93 (0.67–1.28) | 0.83 (0.62–1.12) |
| Winterd | 57,419 | 184 | 1.0 | 1.0 |
| Twin/multiple birth | ||||
| Yes | 2950 | 9 | 0.96 (0.46–2.00) | 0.74 (0.33–1.66) |
| Nod | 235,287 | 724 | 1.0 | 1.0 |
| Born 2+ wk premature | ||||
| Yes | 11,481 | 48 | 1.14 (0.85–1.54) | 1.20 (0.87–1.66) |
| Nod | 172,699 | 597 | 1.0 | 1.0 |
| Parents smoked at home | ||||
| Yes | 122,484 | 459 | 1.16 (0.93–1.44) | 1.24 (1.02–1.51) |
| Nod | 62,619 | 163 | 1.0 | 1.0 |
| Maternal smoking during pregnancy | ||||
| Yes | 30,813 | 128 | 0.92 (0.75–1.12) | 0.97 (0.77–1.21) |
| Nod | 117,540 | 400 | 1.0 | 1.0 |
| Father smoked during pregnancye | ||||
| Yes | 37,773 | 94 | 1.50 (0.99–2.28) | |
| Nod | 19,926 | 29 | 1.0 | |
| Maternal age at birth (y)e | ||||
| 14–19 | 7038 | 11 | 0.96 (0.51–1.82) | |
| 20–24 | 32,884 | 69 | 1.12 (0.80–1.56) | |
| 25–29d | 36,860 | 72 | 1.0 | |
| 30–34 | 24,667 | 57 | 1.22 (0.86–1.73) | |
| 35+ | 17,186 | 28 | 0.88 (0.57–1.37) | |
| P for linear trend | 0.27 | |||
| P for nonlinear trend | 0.02 | |||
| Paternal age at birth(y)e | ||||
| 14–19 | 1430 | 5 | 2.17 (0.87–5.42) | |
| 20–24 | 16,679 | 29 | 0.97 (0.63–1.52) | |
| 25–29 d | 33,971 | 61 | 1.0 | |
| 30–34 | 29,520 | 69 | 1.28 (0.91–1.81) | |
| 35–39 | 17,904 | 44 | 1.36 (0.92–2.00) | |
| 40+ | 14,003 | 22 | 0.94 (0.57–1.54) | |
| P for trend | 0.92 | |||
a
For each factor, the number of cases and participants may not add up to the total number in the study due to missing exposure values.
b
Incident cases are those diagnosed after cohort recruitment (1976 for NHS and 1989 for NHS-II), prevalent cases are the NHS-II cases diagnosed after age 19 and before cohort recruitment in 1989.
c
Controlling for age in months, calendar year, latitude at birth, paternal occupation, sibship size, pack-years of smoking in adulthood, quintile of energy-adjusted vitamin D intake.
d
Reference category.
e
Variables available only in the NHS and therefore only incident cases were confirmed for these analyses.