What are the causes for low birthweight in Japan? A single hospital-based study

Lifetime History of Low Birth Weight Delivery and Cognitive Function in Middle-Aged Parous Women

BACKGROUND AND OBJECTIVES

Pregnancy outcomes such as low birth weight (LBW) delivery may reflect vascular or metabolic dysfunction in mothers and presage future cognitive impairment and dementia. However, the evidence is currently limited. Our objective was to examine the extent to which a lifetime history of LBW delivery was associated with cognitive function in parous middle-aged women.

METHODS

We studied participants from the Nurses' Health Study II, an ongoing longitudinal cohort of female nurses enrolled in 1989. In 2009, participants completed a reproductive history questionnaire. Participants who completed at least one of 2 post-traumatic stress disorder questionnaires were invited to participate in a cognition substudy with 2 waves of baseline data collection (2014 or 2018). We restricted the analysis to participants with one valid cognitive assessment who reported ≥1 birth at 18 years and older. We defined LBW delivery history as having delivered offspring with a birth weight <2,500 g (<5.5 lbs) in any pregnancy. The outcome was a single assessment of cognitive function evaluated with the self-administered Cogstate Brief Battery. The battery comprises 4 tasks, which we used to create 2 composite z-scores measuring psychomotor speed/attention and learning/working memory (higher z-scores = better cognitive function). We used multivariable linear regression models.

RESULTS

The analysis included 15,323 participants with a mean age of 62 (standard deviation: 4.9 years) at cognitive assessment. Among them, 1,224 (8%) had a history of LBW delivery. After adjusting for age at cognitive assessment, race, and ethnicity, participants' education, wave of baseline cognitive assessment, socioeconomic status, and prepregnancy characteristics, women with a history of LBW delivery had lower z-scores in the psychomotor speed/attention (β, -0.06; 95% CI -0.12 to -0.01) and learning/working memory (β, -0.05; 95% CI -0.09 to -0.01) composites than parous women without a history of LBW delivery. We observed a gradient of lower z-scores with an increasing number of LBW deliveries.

DISCUSSION

History of LBW delivery may be marker of future poorer cognition. If confirmed, our findings support future investigations into the value of early preventive efforts targeting women with a history of LBW delivery to reduce the burden of cognitive impairment in women.

Maternal birth weight is an indicator of preterm delivery: the Japan environment and children's study

This study aimed to investigate the association between maternal birth weight (MBW) with preterm delivery (PTD) in the Japanese population. To this end, a total of 78,972 Japanese pregnant women were included in a prospective birth cohort study. Multiple logistic regression and multinominal logistic regression models were applied to investigate the associations of MBW with PTD (delivery from 22 to < 37 weeks of gestation), early PTD (delivery from 22 to < 34 weeks), and late PTD (delivery from 34 to < 37 weeks). The results showed that MBW was inversely associated with PTD, early PTD, and late PTD (p-for-trend < 0.0001, 0.0014, and < 0.0001, respectively). The adjusted odds ratios per each 500 g of MBW decrease were 1.167 (95% confidence interval [CI]: 1.118-1.218) for PTD, 1.174 (95% CI: 1.070-1.287) for early PTD and 1.151 (95% CI: 1.098-1.206) for late PTD. The effect size of the association of MBW with early PTD was similar to that with late PTD. This study demonstrated for the first time an association of a low MBW with PTD, early PTD, and late PTD in a Japanese nationwide cohort.

Factors associated with low birthweight among late preterm singletons in Japan using pregnancy birth registry data

Late preterm (LP, born between 34 0/7 and 36 6/7 weeks of gestation) infants may experience several adverse outcomes, similar to those experienced by low birthweight (LBW, birthweight <2500 g) infants. However, while LP infants are often born with LBW, the association between LP and LBW remains unknown. This study aimed to investigate LBW rate and independent risk factors for LBW in LP singleton neonates. We retrospectively analyzed data of LP singleton neonates, born between 2013 and 2017, from the Japan Society of Obstetrics and Gynecology Successive Pregnancy Birth Registry System. The exclusion criteria included stillbirths and infants with missing data. Logistic regression analyses were performed to investigate maternal and perinatal factors associated with LBW in LP singletons. LBW was observed in 62.5% (n = 35,113) of 56,160 LP singleton births. In the multiple logistic regression analysis, LBW in LP neonates was independently associated with modifiable maternal factors, including pre-pregnancy underweight, inadequate gestational weight gain, and smoking during pregnancy, as well as non-modifiable factors, including younger maternal age, nulliparity, hypertensive disorder of pregnancy, preeclampsia, cesarean section delivery, and female offspring. According to the Japanese pregnancy birth registry data, more than half of LP neonates were LBW. We previously discussed the issue of LBW regarding infants with different backgrounds, as there are many different causes of LBW. Several risk factors should be subdivided and considered for the risk of LP and LBW.

The Associated Factors of Low Birthweight Among Term Singletons in Japan: A Pregnancy Birth Registry Analysis

BACKGROUND

Progress in reducing the global low birthweight (LBW) has been insufficient. Although the focus has been on preventing preterm birth, evidence regarding LBW in term births is limited. Despite its low preterm birth prevalence, Japan has a higher LBW proportion than other developed countries. This study aimed to examine the prevalence of LBW in term singleton births and its associated factors using a national database.

METHODS

We retrospectively analyzed the data of neonates registered in the Japan Society of Obstetrics and Gynecology Successive Pregnancy Birth Registry System who were born 2013-2017. Exclusion criteria included stillbirths, delivery after 42 gestational weeks, and missing data. Logistic regression analyses were performed to investigate the maternal and perinatal factors associated with LBW in term singletons using the data of 715,414 singleton neonates.

RESULTS

The overall prevalence of LBW was 18.3%, and 35.7% of LBWs originated from singleton term pregnancies. Multiple logistic regression analyses indicated that both modifiable and non-modifiable factors were independently associated with LBW in term neonates. The modifiable maternal factors included pre-pregnancy underweight, inadequate gestational weight gain, and smoking during pregnancy, while the non-modifiable factors included younger maternal age, nulliparity, hypertensive disorders of pregnancy, cesarean section delivery, female offspring, and congenital anomalies.

CONCLUSION

Using the Japanese pregnancy birth registry data, more than one-third of LBWs were found to originate from singleton term pregnancies. Both modifiable and non-modifiable factors were independently associated with LBW in term neonates. Prevention strategies on modifiable risk factor control will be effective in reducing LBW worldwide.