Preterm birth and maternal smoking: Risks related to gestational age and onset of delivery

doi:10.1016/S0002-9378(98)70214-5

American Journal of Obstetrics and Gynecology

Volume 179, Issue 4, October 1998, Pages 1051-1055

https://doi.org/10.1016/S0002-9378(98)70214-5 Get rights and content

Abstract

Objective: The object was to examine the effects of smoking on spontaneous and induced very and moderately preterm birth (≤32 and 33-36 completed weeks’ gestation, respectively). Study Design: Live singleton births in Sweden, 1991-1993 (n = 311,977), were examined. Results: Risk of preterm birth consistently increased with amount smoked. Smoking was most heavily associated with increased risks of very preterm birth and spontaneous preterm birth. The highest impact of smoking was seen on risk of spontaneous very preterm birth among women who smoked at least 10 cigarettes/d (odds ratio 1.7). The smoking-related risks of preterm birth remained essentially unchanged after excluding pregnancies with smoking-associated pregnancy complications. Conclusions: There is a dose-related impact of smoking on risk of preterm birth. The fact that the smoking-related risk of spontaneous preterm birth is more pronounced than that of induced preterm birth suggests that smoking is associated with spontaneous preterm labor. (Am J Obstet Gynecol 1998;179:1051-5.)

Section snippets

Description of sample

The Swedish Medical Birth Register, held by the National Board of Health and Welfare, includes more than 99% of all births in Sweden.¹⁰ Information is forwarded to the Birth Register through copies of standardized antenatal and obstetric records generally used in Sweden. From the first antenatal visit, data are prospectively collected and include information about demographic data, previous reproductive history, maternal smoking, and complications during pregnancy, delivery, and the neonatal

Results

Among 311,977 births, 1.0% were born very preterm (≤32 weeks) and 4.2% were moderately preterm (33-36 weeks) (Table I).

. Rates of preterm birth by maternal characteristics among Nordic women: Live single births in Sweden, 1991-1993

Maternal characteristics	Total births (No.)	≤32 wk (%, n = 3059)	33-36 wk (%, n = 13,081)
Maternal age
10-19 y	7,538	1.3	5.9
20-24 y	64,848	1.0	4.5
25-29 y	122,001	0.8	4.0
30-34 y	80,519	1.0	3.8
≥35 y	37,071	1.3	4.9
Parity
1	127,527	1.2	5.1
2-3	163,492	0.8	3.4
≥4	20,958	1.2	4.9
Smoking
Nonsmoking	228,519	0.8	3.9

Comment

This study confirms results from other large epidemiologic studies that smoking is significantly associated with preterm birth.1, 3, 5, 6, 7, 8 Also in accordance with the results of previous investigations,5, 6 we found that smoking was associated more with increased risk of very preterm birth (≤32 weeks’ gestation) than with increased risk of moderately preterm birth (33-36 weeks’ gestation) and that smoking was associated more with spontaneous than with induced preterm birth.³

It has been

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A total of 136 women were recruited, of whom 8 were lost to follow-up and 7 were excluded. Of the remaining 121 patients, 22 had a time to delivery <7 days and 31 had a time to delivery <14 days, and 30 deliveries occurred with a gestational age at delivery ≤34 weeks and 55 with a gestational age at delivery ≤37 weeks. Univariate binary logistic regression models fitted with the log transformation of interleukin-6 showed the greatest F2-scores in most studies, which outperformed those of models fitted with placental alpha microglobulin-1 (log[interleukin-6] vs placental alpha microglobulin-1 in time to delivery <7 days: 0.38 vs 0.30; time to delivery <14 days: 0.58 vs 0.29; gestational age at delivery ≤34 weeks: 0.56 vs 0.29; gestational age at delivery ≤37 weeks: 0.61 vs 0.16). Multivariate logistic regression models fitted with imbalanced data sets outperformed most univariate models (F2-score in time to delivery <7 days: 0.63; time to delivery <14 days: 0.54; gestational age at delivery ≤34 weeks: 0.62; gestational age at delivery ≤37 weeks: 0.73). The performance of prediction of multivariate models was drastically improved when data sets were balanced, and was maximum for time to delivery <7 days (F2-score: 0.88±0.2; positive predictive value: 0.86±0.02; negative predictive value: 0.89±0.03).
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Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous chemicals with mechanisms of toxicity that include endocrine disruption. We examined associations of prenatal urinary PAH with spontaneous preterm birth (PTB) and gestational age (GA) at birth. We also assessed whether infant sex modifies the association of PAH exposure with spontaneous PTB and GA at birth.
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In labor, the MPS group (n = 115) had higher rates of meconium stained amniotic fluid (MSAF, p < 0.001) and non-reassuring fetal heart-rate (NRFHR,p = 0.006), compared to controls (n = 115). Neonates in the MPS group had higher rates of undiagnosed FGR (p = 0.01) and NICU admissions (p = 0.004). The MPS group had higher rates of placental-hypoplasia (p = 0.02) and fetal vascular malperfusion (FVM) lesions (p = 0.04). In regression analysis MPS was associated with FVM lesions independent of background confounders (aOR = 1.24 95% CI 1.10–2.65).
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^☆: From the Division of Obstetrics and Gynaecology, Danderyd Hospital, Karolinska Institutet,^a and the Department of Cancer Epidemiology, Uppsala University Hospital.^b

^☆☆: Reprint requests: Nina B. Kyrklund-Blomberg, MD, Karolinska Institutet, Danderyd Hospital, Division of Obstetrics and Gynaecology, S-182 88 Danderyd, Sweden.

^★: 0002-9378/98 $5.00 + 06/1/91413

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Preterm birth and maternal smoking: Risks related to gestational age and onset of delivery☆,☆☆,★

Abstract

Section snippets

Description of sample

Results

Comment

Am J Obstet Gynecol

Am J Obstet Gynecol

Am J Obstet Gynecol

J Clin Epidemiol

Am J Obstet Gynecol

Lancet

Am J Obstet Gynecol

Am J Obstet Gynecol

Epidemiology of preterm birth

Epidemiol Rev

Multicenter randomized, controlled trial of a preterm birth prevention program

Am J Obstet Gynecol

Factors associated with preterm birth in Cardiff, Wales. I. Univariable and multivariable analysis. II. Indicated and spontaneous preterm birth

Am J Obstet Gynecol

Smoking and drinking during pregnancy: their effects on preterm birth

JAMA