双胎分娩34〜40週の出産結果に及ぼす 胎児の性、性組合せ、経産の影響 野中浩一(帝京大・医・衛生公衛) 今泉洋子(兵庫大学附属研究所) 【目的】 日本全体の双胎出産のデータ(79-94年) 分娩週数 児の性 性組み合わせ 初産・経産の別 出産数 死産割合 出産時体重 【資料と方 法】 ● 1979〜94年の人口動態統計の双胎分 出生票n=284,259 と 死産票n=30,803 計n=315,062 ● ペア作成 155,094組(310,188人)⇨ ● 出産時体重情報が入手できた出産(n=313,892) ● ● 98.5% 体重の推定 79-91年 100g単位、切り捨て(2500gは別掲) 92-94年 1g単位 ※ 79-91年については階級の中央値を代用して計算 分娩時在胎週数:34-40週に限定 出産数割合(種類別の相対値、%) 30% 単胎児 25% 双胎児 20% トピック 3 品胎児 15% 10% 5% 0% 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 出産時の妊娠週数(満・週) 図1 単胎、双胎、品胎の出産時妊娠週数分布 1.0000 死産児割合 0.1000 トピック 2 0.0100 単胎児 0.0010 双胎児 品胎児 0.0001 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 出産時の妊娠週数(満・週) 図2 出産時妊娠週数別死産児割合 4000 平均出生時体重 (g) 単胎児 3000 トピック 1 双胎児 品胎児 2000 1000 0 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 出産時の妊娠週数(満・週) 図3 出産時妊娠週数別平均出生体重(g) Mean twin birth weight by gestational weeks, sex, and sex combination, all Japan, 1979-94 (Stillbirths) 3500 Birth weight (g) 3000 M ale (M ale+Male) M ale (M ale+Female) Female (M ale+Female) Female (Female+Female) 2500 2000 1500 1000 500 0 -25 26-27 28-29 30-31 32-33 34-35 36-37 Gestational week at birth (weeks) 38-39 40-41 42+ Mean triplet birth weight by gestational weeks and sex of child, all Japan (Stillbirths, sex-unknown excluded) 2500 male female 2000 malesm 1500 1000 500 0 -23 24-25 26-27 28-29 30-31 32-33 34-35 gestational week (weeks) 36-37 38-39 40+ Triplet pregnancy 38weeks Period when male fetus (or embryo) is more susceptible to growth retardation Twin pregnancy 26weeks Period when male fetus (or embryo) is more susceptible to growth retardation Singleton pregnancy ? Conception Gestation period Birth Number of twin births and stillbirth rate, all Japan, 1979-1994 30000 15 Live births Stillbirths 25000 20000 10 15000 10000 5 5000 0 0 79 80 81 82 83 84 85 86 87 Year 88 89 90 91 92 93 94 Stillbirth rate (%) Number (per year) Stillbirth rate (%) Mean birth weight of twin according to year, all Japan, 1979-1994 3000 Birth weight (g) 2500 2000 Live births Stillbirths 1500 1000 500 0 78 80 82 84 86 88 Year 90 92 94 96 Mean twin birth weight by gestational weeks and birth year period, all Japan (Live births) 1979-82 1983-86 1987-90 1991-94 3000 Birth weight (g) 2500 2000 1500 1000 500 0 -25 26-27 28-29 30-31 32-33 34-35 36-37 38-39 Gestational weeks at birth (weeks) 40-41 42+ Mean twin birth weight by gestational weeks and sex (Live), all Japan, 1979-94 3000 M ale Female Birth weight (g) 2500 2000 1500 1000 500 0 -25 26-27 28-29 30-31 32-33 34-35 36-37 38-39 Gestational weeks at birth (weeks) 40-41 42+ 15000 2nd+ Like-sexed M ale Female Number of births 1st Like-sexed Male 10000 Female 2nd+ Unlike-sexed M ale Female 5000 1st Unlike-sexed M ale Female 0 33 34 35 36 37 38 39 Gestation period (weeks) 40 41 2001fig.d.cg3 3000 2nd+ Unlike-sexed M ale Female 2750 Birth weight (g) 2nd+ Like-sexed M ale Female 2500 1st Unlike-sexed M ale Female 2250 1st Like-sexed Male Female 2000 1750 33 34 35 36 37 38 39 Gestation period (weeks) 40 41 2001fig.d.cg3 3000 Female Male Birth weight (g) 2750 2500 2250 2000 1750 33 34 35 36 37 38 2nd+ Unlike-sexed 2nd+ Like-sexed 1st Unlike-sexed 1st Like-sexed 39 40 41 33 34 35 Gestation period (weeks) 36 37 38 39 40 41 6.0% 2nd+ Like-sexed M ale Stillbirth rate (%) 5.0% Female 4.0% 1st Like-sexed Male Female 3.0% 2nd+ Unlike-sexed M ale 2.0% Female 1.0% 1st Unlike-sexed M ale Female 0.0% 33 34 35 36 37 38 39 40 41 Gestation period (weeks) 2001fig.d.cg3 6.0% Male Stillbirth rate (%) 5.0% 4.0% 3.0% 2nd+ Like-sexed 1st Like-sexed 2.0% 2nd+ Unlike-sexed 1.0% 1st Unlike-sexed 0.0% 32 34 36 38 40 42 Gestation period (weeks) 2001fig.d.cg3 4.0% Female Stillbirth rate (%) 3.0% 2nd+ Like-sexed 2.0% 1st Like-sexed 2nd+ Unlike-sexed 1.0% 1st Unlike-sexed 0.0% 32 34 36 38 40 42 Gestation period (weeks) 2001fig.d.cg3 15000 2nd+ Like-sexed M ale Female Number of births 1st Like-sexed Male 10000 Female 2nd+ Unlike-sexed M ale Female 5000 1st Unlike-sexed M ale Female 0 33 34 35 36 37 38 39 Gestation period (weeks) 40 41 2001fig.d.cg3 Live births Twin births in Japan, 1979-1994 30000 Number of Live Males 25000 Number of Live Females 20000 15000 10000 5000 Gestation Weeks 42 +w 41 40 39 38 37 36 35 30 -3 1 32 -3 3 34 9 24 -2 3w 0 -2 Number of live births 35000 55.0% Like-sexed, 1st Male proportion (%) 54.0% Like-sexed, 2nd or later テーマについて 53.0% Unlike-sexed, 1st 52.0% Unlike-sexed, 2nd or later 51.0% テーマ (自分の主張) の説明 50.0% 49.0% 48.0% 47.0% 46.0% 45.0% 33 34 35 36 37 38 39 Gestation period (weeks) 40 41 まとめ 出産時体重は妊娠34〜40週で単調に増加していたが、初産・ 経産の別、男女別のほかに、異性・同性ペア別による違いが 観察された。すなわち、単胎と同様に、経産が初産より重く、男 児が女児より重かったほか、同じ性でも、ペアが同性より異性 の組合せのほうで重くなっていた。 死産率は、全体では妊娠38週の分娩で最低になり、男児が 女児よりやや高いが、ペアが同性か異性かの違いのほうが影 響が大きく、異性の組み合わせで低かった。これらの結果は、 同性双胎に含まれる1卵性双胎が影響しているものと思われ る。経産でやや高くなるのは年齢が交絡している可能性があ る。 なお、同性双生児の場合、女児では男児よりも分娩週数が長 くなる傾向があり、死産率が最低になるのも妊娠39週での分 娩であり、全体より1週程度遅くなっていた。 Mean twin birth weight by gestational weeks, sex and sex combination, all Japan, 1979-94 (Live births) 3000 M ale (M ale+Male) M ale (M ale+Female) Female (M ale+Female) Female (Female+Female) Birth weight (g) 2500 2000 1500 1000 500 0 -25 26-27 28-29 30-31 32-33 34-35 36-37 38-39 Gestational week at birth (weeks) 40-41 42+ Mean twin birth weight by gestational weeks, sex and type of birth, all Japan, 1979-94 (Live births) 3500 3000 M ale(Live+Live) M ale (Live+Still) Female (Live+Live) Female (Live+Still) Birth weight (g) 2500 2000 1500 1000 500 0 -25 26-27 28-29 30-31 32-33 34-35 36-37 38-39 Gestational week at birth (weeks) 40-41 42+ Mean twin birth weight by gestational weeks, sex and type of birth, all Japan, 1979-94 (Live births) 3500 3000 M ale(Live+Live) M ale (Live+Still) Female (Live+Live) Female (Live+Still) Birth weight (g) 2500 2000 1500 1000 500 0 -25 26-27 28-29 30-31 32-33 34-35 36-37 38-39 Gestational week at birth (weeks) 40-41 42+ Proportion of gestational weeks for twin births, all Japan (Live births) Year period 1979-1982 1983-1986 1987-1990 1991-1994 0 10 20 30 40 50 60 70 80 90 Percentage -25w 26-27w 28-29w 30-31w 32-33w 34-35w 36-37w 38-39w 40-41w 42+w 100 Proportion of gestational weeks for twin births, all Japan (live- + stillbirths) Year period 1979-1982 1983-1986 1987-1990 1991-1994 0 10 20 30 40 50 60 70 80 90 Percentage -25w 26-27w 28-29w 30-31w 32-33w 34-35w 36-37w 38-39w 40-41w 42+w 100 Mean birth weight of twin by year, type of birth, and sex, all Japan, 1979-1994 3000 Birth weight (g) 2500 2000 Live births, Male Live births, Female 1500 Stillbirths, M ale Stillbirths, Female 1000 500 0 78 80 82 84 86 88 Year 90 92 94 96
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