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In a randomized trial of 987 pregnant women, most of whom had pre-existing hypertension, about the same percentage of women in the tight and loose blood pressure control groups experienced a loss of pregnancy or gave birth to a child in need of high-level neonatal care (30.7% and 31.4%, respectively), according to of the University of British Columbia, and colleagues.

However, severe hypertension rates were higher among those in the less-tight control arm (40.6% versus 27.5%), the researchers reported in the .

"Randomized trials of treatment of mild, chronic hypertension in pregnancy have consistently failed to show improvements in major complications," , and , wrote in an editorial in .

Solomon and Greene suggest that the jury is still out on optimal control of hypertension during pregnancy as most investigations haven't been properly designed or powered to yield consistent results.

And, they observed, the current study wasn't powered to show differences in some relevant outcomes, such as intrauterine growth restriction rates or in frequencies of maternal or fetal death.

Study Details

The Control of Hypertension in Pregnancy Study (CHIPS) was an unblinded, randomized, controlled trial involving 987 women with nonsevere, nonproteinuric pre-existing or gestational hypertension from 111 clinics in 16 countries. Recruits were enrolled from 2009 to 2012. Three-quarters of those enrolled had pre-existing high pressure.

The eligibility cut points were a diastolic blood pressure of 90-105 mmHg for women not on antihypertensives, or 85-105 mmHg for those receiving treatment, and a pregnancy ranging from 14 weeks to just under 34 weeks of gestation. Only singleton pregnancies were included.

The women were randomized into a "less-tight" arm with a target of 100-104 mmHg diastolic blood pressure and a "tight" arm with a target of 81-85 mmHg diastolic. Women in each group were expected to adhere to treatment to achieve 5 mmHg above or below the target value of 100 mmHg or 85 mmHg.

Magee's team reported that treatment adherence was similar between the less-tight and tightly controlled groups (74.1% versus 73.4%, respectively).

Throughout the trial, women in the less-tight group had an average of 5.8 mmHg higher systolic blood pressure (95% CI 4.5-7.0, P<0.001) and 4.6 mmHg diastolic (95% CI 3.7-5.4, P<0.001) compared with the tight-control group. A total of 73.4% of women in the less-tight group, and 92.6% in the tight group, took antihypertensive medication before delivery, and those rates dropped to 65.5% and 78.3%, respectively, after delivery (P<0.001).

Maternal health was followed for 6 weeks, and infant health was followed for 28 days postpartum, or until hospital discharge. Primary outcome measures looked at pregnancy loss and high-level neonatal care for longer than 48 hours. Secondary outcome measures looked at serious maternal and newborn complications, and fetal growth.

Only six women were lost to follow-up or dropout, although some data were missing for 25 women completing the trial.

Results

Pregnancy loss occurred among 3.0% of women in the less-tight group, and 2.7% of women in the tight control group (adjusted odds ratio 1.14, 95% CI 0.53-2.45). Lengthy high-level neonatal care barely differed between groups, as this was indicated for 29.4% the infants born to women in the less-tight arm, and 29.0% of infants born to women in the tight control arm (AOR 1.00, 95% CI 0.75-1.33).

No differences were seen between groups for gestational age at the time of delivery or C-section delivery.

The researchers reported that most fetal mortalities, 2.8% in the less-tight group and 2.3% among tight group, were stillbirths and most of the high-level neonatal care resulted from premature births, which were also similar among groups -- gestational age at delivery averaged 36.8 weeks in the less-tight group and 37.2 weeks in the tight-control group.

Serious maternal complications, such as transient ischemic attack or stroke, pulmonary edema, renal failure, or transfusion, occurred in 3.7% of the women in the less-tight group and 2.0% of the women in the tight group (AOR 1.74, 95% CI 0.79-3.84). Including both groups, 24 out of the 28 total incidents were transfusions.

Severe hypertension, defined as systolic blood pressure ≥160 mmHg, represented the greatest disparity between groups. Among women in the less-tight group, 40.6% exceeded the threshold versus 27.5% of women in the tight controlled group (AOR 1.80, 95% CI 1.34-2.38).

Solomon and Greene noted that the study protocol encouraged the use of labetalol to reach target blood pressure, but that one-third of the women weren't treated with this particular drug, and that Magee's team didn't report outcome differences between antihypertensive medications or doses.

Solomon and Greene suggested that reducing a pregnant woman's hypertension doesn't necessarily translate to lower rates of preeclampsia and other serious maternal complications, but that it can result in putting the fetus at risk.

However, they concluded that the Magee study reinforced evidence that tight control of hypertension doesn't put the baby at risk.

The study authors noted that the inclusion of women who had pre-existing or gestational hypertension could be considered a limitation despite the lack of differences between groups in primary and secondary outcomes.

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