Tdap vaccine: No connection found to microcephaly

December 7, 2016

A study looks at whether receiving the Tdap vaccine in pregnancy increases the risk of microcephaly. Plus: Are younger or older women more at risk of stroke during pregnancy?

According to a research letter in JAMA, the tetanus, diphtheria, and acellular pertussis (Tdap) vaccine may not be linked to an increased risk of microcephaly or other structural birth defects.

Researchers looked at singleton live births from January 2007 to September 2013 at 7 Vaccine Safety Datalink sites in Northern California, Southern California, Colorado, Minnesota, Oregon, Washington, and Wisconsin. They compared the prevalence of structural birth defects among infants born to women who had received the Tdap vaccine during pregnancy and those born to women who were unvaccinated. Pregnancies were found in electronic healthcare data using a validated algorithm. Each woman involved had to be continuously insured from 6 months prior to her last menstrual period until 6 weeks postpartum and had to have 1 or more outpatient visits to ensure that all diagnoses were accounted for. The infants had to have their birth weight and gestational age data recorded and they had to be insured for 4 months of their first year with 1 or more outpatient visits. Any infants with exposures known to increase the risk of structural defect, such as use of teratogenic medication, were excluded from the study.

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Three vaccine windows were examined: less than 14 weeks’ gestation, the current recommendation of 27 to 36 weeks’ gestation, and any other gestational week. Diagnostic codes were used to identify any structural effect, major structural effect, or microcephaly.

The study covered 324,463 live singleton births. The maternal Tdap vaccine was not significantly associated with increased risk of microcephaly when it vaccine was given at less than 14 weeks’ gestation (n = 3321; adjusted prevalence ratio [APR], 0.96 [95% confidence interval {CI}, 0.36-2.58]). Similar results were seen with vaccination given between 27 and 37 weeks (n = 20568; APR, 1.01 [95% CI, 0.63-1.61]) or any other week of gestation (n = 41 654; APR, 0.86 [95% CI,0.60-1.24]). Analyses for any structural defect and selected structural defects were similar.

Investigators concluded that the Tdap vaccine continues to be safe in pregnancy and they support the current recommendation for routine Tdap vaccination during pregnancy.

NEXT: Who is most at risk of stroke in pregnancy?

 

Who of is most at risk of stroke in pregnancy?

While older women may be at overall higher risk of pregnancy complications, a new study in JAMA Neurology indicates that younger women may be at greater risk of suffering a stroke during that period.

Researchers did a retrospective cohort analysis using billing data from 2003 to 2012 in the New York State Department of Health Statewide Planning and Research Cooperative System. They identified all women aged 12 to 55 years who were admitted with transient ischemic attack, ischemic stroke, intracerebral hemorrhage, subarachnoid hemorrhage, cerebral venous thrombosis, and non-specified pregnancy-associated stroke, according to their billing code. Pregnant or postpartum women were identified by admission with a delivery code, admission with a pregnancy code but no delivery code, and admission with a postpartum code but no delivery code.

There were 19,146 women who were hospitalized with stroke of whom 797 occurred during pregnancy or postpartum. Overall median (interquartile range) age of the women was 31 (25-35) years in those with a pregnancy-associated stroke and 48 (41-52) years in those with a nonpregnancy-associated stroke. Incidence of a pregnancy-associated stroke in women who aged 12 to 24 years was 14 events per 100,000 pregnant/postpartum women while the incidence of nonpregnancy-associated stroke was 6.4 per 100,000 nonpregnant women (incidence risk ratio [IRR], 2.2; 95% confidence interval [CI], 1.9-2.6). For women aged 25 to 34 it was 21.2 per 100,000 versus 13.5 per 100,000 (IRR, 1.6; 95% CI, 1.4-1.7) and in women aged 35 to 44 years: 33 per 100 000 versus 31 per 100,000 (IRR, 1.1; 95% CI, 0.9-1.2). Among women aged 45 to 55 years it was 46.9 per 100,000 vs 73.7 per 100,000 (IRR, 0.6; 95% CI, 0.3-1.4).

Strokes associated with pregnancy accounted for 18% of strokes in women aged younger than 35 years and only 1.4% in women aged 35 to 55. In addition, women in the nonpregnancy-associated stroke group had more risk factors such as chronic hypertension and active smoking than the pregnancy-associated stroke group. They also had higher mortality (age <35 years: 288 [11.3%] vs 37 [6.5%], P < .001; age 35-55: 2121 [13.4%] vs 14 [6.1%], P < .001).

Some of the study limitations noted by the authors include that ICD-9 billing codes lack specificity particularly with pregnancy-associated strokes. They validated the codes by reviewing the medical records of the women with pregnancy-associated stroke and confirmed a low false-negative rate. They also noted that they could not determine the timing of pregnancy-associated stroke. In addition, there were some risk factors and medication effects that were not accounted for in the analysis. Study strengths included the diversity of the population as the system used to collect the data is a comprehensive data set for the state of New York and captures all stroke admissions in the state. New York has a diverse population, covers the socioeconomic spectrum, and features both urban and rural areas.

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Researchers concluded that younger women, not older women, were more likely to have an increased risk of stroke during the course of pregnancy and into postpartum when compared to women of a similar age who were not pregnant.