Risk Factors for Low Birth Weight Infants in Japanese Pregnancies: A One-year Study of 2551 Cases in Tokyo

Abstract

Background: The rate of low-birth weight infants in Japan has been increasing. Being underweight and increasing maternal age are risk factors for delivering low birthweight infants. Currently, pregnant Japanese women exhibit these risk factors for delivering low birthweight infants; however, little research has been conducted. This study aimed to investigate the associations between pregnancy characteristics in Japanese women and low birth weight infants. Methods: We enrolled 2551 pregnant women at >36 weeks of gestation and who delivered in metropolitan Tokyo. Pre-pregnancy body mass index was categorized using the World Health Organization classification. Gestational weight gain and birth weight were categorized based on the guidelines of the Ministry of Health, Labour and Welfare, Japan. The differences in pregnancy characteristics among three birth-weight categories,i.e., low birth weight, normal, and macrosomia, were assessed using the chisquare test. The risk ratios of low birth weight were estimated using logistic regression analysis. Results: In Japanese pregnancies, birth weight was associated with gestational week at delivery, gestational weight gain, pre-pregnancy body mass index, sex, parity, and maternal age (P<0.05). In particular, the risk of low birth weight increased with advanced maternal age (odds ratio=1.97), insufficient gestational week at delivery (odds ratio=9.00), low gestational weight gain (odds ratio=2.76), and female infant (odds ratio=2.06). Further, it decreased in multiparous women compared with that in primiparous women (odds ratio=0.57). Conclusions: These findings suggest that pregnant Japanese women who are ≥40 years old with a gestational weight gain of <7.0 kg, <37 gestational weeks at delivery, female baby, and primiparous should be checked carefully during the gestational period. In order to decrease the risk of low birth weight babies, women should be educated early about childbearing and pregnancy.

Hypertensive Disorders during Pregnancy (HDP), Maternal Characteristics, and Birth Outcomes among Japanese Women: A Hokkaido Study

“…Several studies have suggested primiparity as a risk factor for PTB [ 50 ]; however, primiparity was found to be associated with SGA, term-SGA, and LBW in our study. Our findings are consistent with a previous Japanese study, which indicated that the risk of LBW is lower among multiparous women [ 21 ]. Our findings are consistent with other studies that showed an association between birth outcomes and maternal characteristics, such as LBW babies and PTB with maternal age [ 43 , 51 ] and LBW and PTB with maternal BMI [ 30 , 52 ].…”

“…In Japan, the number of underweight women, mainly in their 20s and 30s, has significantly increased. A survey conducted by the Ministry of Health, Labor and Welfare showed that about 25% of Japanese women of reproductive age are underweight (BMI < 18.5 kg/m 2 ) and are at risk of delivering LBW infants and SGA infants [ 21 , 46 , 47 ]. Our study showed that pre-pregnancy BMI (<18.5 kg/m 2 ) showed a strong association with SGA, term SGA, PTB, and LBW.…”

“…The recent trend in Japan shows a declining mean birth weight from 3200 g to 3000 g (3050 g for boys; 2960 g for girls) within 43 years (1975 to 2018) [ 18 , 19 ]. Similarly, Japan’s maternal age at childbirth is increasing rapidly, with the mean age at first birth at 30.7 years in 2018, which was 25.7 years in 1975 [ 20 , 21 , 22 ]. A gradual trend towards delayed motherhood is seen in several countries with low fertility, such as Italy, Spain, China, Latin America, and North Africa [ 23 ].…”

Epidemiology of low birth weight in Iran: A systematic review and meta-analysis

“…In evaluating the effect of gender on LBW, we found that the prevalence of LBW in females was significantly higher than males. In a study conducted in Japan, there was a significant relationship between female gender and low birth weight [111], and it was also found that the mean birth weight of male infants was higher than that of female infants [112].…”

Prenatal Nicotine Exposure Induces Low Birthweight and Hyperinsulinemia in Male Rats

“…There are various etiologies of low birthweight ( 1 ), and smoking by pregnant mothers is one such causes ( 2 , 3 ). Smoking by pregnant mothers remains a major public health concern.…”