抄録
本研究では,自然出産を提唱してきたA診療所における1972〜2007年までの36年間の分娩記録17,687件を基に,分娩時の母体年齢,在胎週数,分娩時刻や出生体重の推移を明らかにした。また,開院10年目頃から変化した出産管理の方法が,どう周産期のアウトカムに影響を与えているのかを考察した。その結果,分娩時の母体年齢の推移は,1972〜1981年は約50%の人は25歳までに出産していたものが,2002〜2007年は約50%の人は34歳までに出産し,5歳上昇し,約80%の人は34歳までに出産していた。平均在胎週数の推移は,1979年を境に在胎週数は有意(P<0.01)に短くなっており,同診療所の妊婦健診に超音波診断が導入された時期とほぼ一致していることが明らかになった。分娩時刻の推移は,1972〜1981年にかけては,午前8時〜午後4時までが分娩時刻のピークであったものが,1982年以降の30年間は午前0時〜午前8時までが分娩時刻のピークとなり,自然出産を提唱し始めた1982年を境に有意(P<0.01)に分娩時刻に差がみられた。平均出生体重の推移は,出生体重の分布図を10年ごとにみた場合,1972〜1991年の20年間は出生体重の分布幅は大きかったが,1992年頃から徐々に偏差が狭くなり,2002年以降は出生体重の平均値あたりに分布が集中し,とくに偏差が狭くなっていることがわかった。以上,A診療所における周産期のアウトカムは,出産管理の内容を変化させた年次によってその様相が異なっていることが明らかになった。
This study examined the records of 17,687 births that took place from 1972 through 2007 at Clinic A, a clinic that has promoted natural childbirth, to determine what changes have taken place over these 36 years in maternal age, length of gestation, time of birth, and birth weight. Some ten years after the clinic opened, the guiding principle for care changed from medical intervention to natural birth. The present study also considers how this development has affected perinatal outcomes. Our examination of the data revealed the following trends. Regarding maternal age at the time of childbirth, there has been a notable increase: in the period from 1972 to 1981, 50% of women had finished childbearing by age 25, whereas in the period from 2002 to 2007, 50% of women had finished childbearing by age 30, an increase of 5 years. In the latter period, 80% of women had finished childbearing by age 34. Regarding the average length of gestation, we found a significant (P<0.01) decrease after 1979, a shift that roughly coincides with the introduction of ultrasound examinations in the antenatal checkups conducted at the clinic. A shift was also noted in the time of birth. From 1972 through 1981, the distribution shows a peak between 8AM and 4PM, but in the 30 years since 1982, the peak has been between midnight and 8AM, indicating a significant ((P<0.01) difference before and after 1982, when the clinic began to encourage natural childbirth. Birth weights were examined by comparing distribution diagrams of birth weights over a series of 10-year periods. In the 20 years from 1972 through 1991, birth weights covered a wide range, but from about 1992, the spread gradually grew smaller. From 2002 onwards, the range has been very narrow, with birth weights clustered around the median value. These changes clearly indicate that perinatal outcomes at Clinic A have changed coinciding with changes to antenatal care and childbirth management.
