吸烟孕妇补充VC可改善新生儿肺功能

旧金山(EGMN)——美国胸科学会(ATS)国际会议上报告的一项随机双盲研究显示，与妊娠期服用安慰剂的吸烟女性所生育的新生儿相比，妊娠期服用维生素C补充剂的吸烟女性的新生儿肺功能明显更好。

这项研究由波特兰俄勒冈卫生科学大学的Cindy T. McEvoy博士及其同事进行，纳入年龄≥15岁、单胎胎龄不足22周的妊娠吸烟女性。排除以下女性：多胎妊娠或胎儿先天性畸形、目前使用违禁药品或滥用酒精、肾结石史、胰岛素依赖性糖尿病、自上次月经后一直服用维生素C者。在治疗开始前，要求受试者每天服用1次安慰剂，那些服用安慰剂剂次不足75%的依从性差者不得进入随机分组阶段。76名吸烟女性随机接受500 mg/d维生素C治疗，83名吸烟女性随机接受安慰剂治疗，治疗持续至分娩。研究期间对这些女性实施戒烟教育，但她们均拒绝戒烟。非随机对照组入选76名非吸烟女性。

研究开始时，两个吸烟组在孕妇年龄、保险范围、可替宁水平、服药依从性、哮喘病史和每天吸烟≥10支者的比例方面均无显著差异。两个吸烟组的婴儿人口学特征与非吸烟对照组相似，包括出生体重、分娩时胎龄、性别、32周胎龄前分娩率和阴道分娩率。

随机分组时，两个吸烟组产妇的血浆抗坏血酸水平显著低于非吸烟组。妊娠中期时，维生素C组的抗坏血酸水平与非吸烟组相似(分别为59和58 μmol/L)，而安慰剂组的抗坏血酸水平仍明显较低(40μmol/L)。

安慰剂组婴儿的肺流量(潮式呼气流量达峰时间与呼气时间之比)为0.345，显著低于维生素C组(0.383)和非吸烟组(0.399)。

研究者还发现，安慰剂组新生儿的被动呼吸力学或呼吸系统顺应性为1.2 Crs/kg，显著低于维生素C组(1.32 Crs/kg)和非吸烟组(1.36 Crs/kg)。出生后48 h对新生儿进行肺功能检查发现，维生素C组新生儿与对照组相似，并且这两组均优于安慰剂组。治疗对呼吸频率无显著影响。

研究者表示，未考察对婴儿给予维生素C补充剂的策略，这一策略值得进一步研究。

该研究证实了既往的非人灵长类动物研究的结果，后者显示每天服用1次维生素可阻断尼古丁对胎儿肺发育和新生儿肺功能的影响(Am. J. Respir. Crit. Care Med. 2005;171:1032-9)。

研究者计划在这些婴儿1岁时再次进行肺功能检查，并与喘息发作等临床预后进行比较。他们目前已从美国国立心肺血液研究所获得招募新队列的资金，并将测定新生儿用力呼气流量(主要终点)。

该研究获美国国立心肺血液研究所资助。McEvoy博士声明无经济利益冲突。

爱思唯尔  版权所有

BY SHERRY BOSCHERT
Elsevier Global Medical News
Breaking News

SAN FRANCISCO (EGMN) – Newborn lung function was significantly better in pregnant smokers who took vitamin C supplements, compared with smoking mothers on placebo, in a double-blind trial that randomized 179 women.

Among 159 infants who underwent pulmonary function tests at around 48 hours of age, results in the 76 newborns of smokers getting vitamin C were similar to results for 76 newborns of nonsmoking women in a nonrandomized comparison group. Both subgroups had better pulmonary function than did the 83 newborns of placebo-treated smokers, Dr. Cindy T. McEvoy and her associates reported at an international conference of the American Thoracic Society.

“We speculate that vitamin C supplementation in pregnant women who cannot quit smoking is helpful,” said Dr. McEvoy of Oregon Health and Science University, Portland.

The current study randomized pregnant smokers aged 15 years and older, and prior to 22 weeks gestation of their singletons, to take 500 mg/day of vitamin C or placebo until delivery. The women were counseled throughout the trial to quit smoking but declined to do so.

Maternal plasma levels of ascorbic acid were significantly lower in the two smoking groups at randomization, compared with levels in nonsmokers. By mid-gestation, ascorbic acid levels in the vitamin C group were similar to levels in nonsmokers (59 and 58 micromol/L, respectively), but levels in the placebo group remained significantly lower (40 micromol/L).

Infant pulmonary flow volume, characterized as a ratio of the time to peak tidal expiratory flow to expiratory time, was significantly lower in the placebo group (0.345), compared with the vitamin C group (0.383) and the nonsmoking group (0.399), Dr. McEvoy said.

Investigators also measured the newborns’ passive respiratory mechanics, or compliance of the respiratory system (Crs/kg), and found significantly lower results in the placebo group (1.2 Crs/kg), compared with the vitamin C group (1.32 Crs/kg) or the nonsmoking group (1.36 Crs/kg).

Treatment did not significantly affect respiratory rate.

There were no significant differences between the randomized groups at the start of the study in characteristics including maternal age, insurance coverage, cotinine levels, medication adherence, history of asthma, or the proportion of women smoking 10 or more cigarettes per day.

Infant demographics were similar in the two groups of smokers and the reference group of nonsmokers, including birth weight, gestational age at delivery, sex, rate of delivery before 32 weeks’ gestation, and rate of vaginal delivery.

The investigators plan to perform infant pulmonary function tests again when the study babies are 1 year old and compare it with clinical outcomes such as episodes of wheezing. They have secured support from the U.S. National Heart, Lung, and Blood Institute to randomize a new cohort and measure newborn forced expiratory flows as the primary outcome, she said.

The investigators did not give vitamin C supplementation to infants, but that strategy may deserve study as well, Dr. McEvoy said.

The study excluded pregnancies with multiple gestation or fetal congenital anomalies and women who currently used illicit drugs or abused alcohol, had a history of kidney stones, had insulin-dependent diabetes, or who had been taking vitamin C daily since their last menstrual period. Before the treatment period began, participants were asked to take a daily placebo; those who complied with fewer than 75% of placebo doses were excluded from randomization.

Approximately 12% of U.S. women smoke during pregnancy and at least 500,000 newborns each year have been exposed to smoke in utero. Previous studies have shown that infants of smokers have worse lung function at birth and a higher risk of developing lung diseases, including asthma, bronchitis, and pneumonia, compared with infants of nonsmokers.

The current findings support evidence from nonhuman primates that daily vitamin C can block the in utero effects of nicotine on lung development and newborn pulmonary function (Am. J. Respir. Crit. Care Med. 2005;171:1032-9).

Dr. McEvoy reported having no financial disclosures. The U.S. National Heart, Lung, and Blood Institute funded the study.