Post-term birth and the risk of behavioural and emotional problems in early childhood
Abstract
Background Post-term birth, defined as birth after pregnancy duration of 42 weeks, is associated with increased neonatal morbidity and mortality. The long-term consequences of post-term birth are unknown. We assessed the association of post-term birth with problem behaviour in early childhood.
Methods The study was performed in a large population-based prospective cohort study in Rotterdam, The Netherlands. Pregnant mothers enrolled between 2001 and 2005. Of a cohort of 5145 children, 382 (7%) were born post-term, and 226 (4%) were born preterm. Parents completed a standardized and validated behavioural checklist (Child Behavior Checklist, CBCL/1.5–5) when their children were 1.5 and 3 years old. We examined the relation between gestational age (GA) at birth, based on early fetal ultrasound examination, and problem behaviour with regression analyses, adjusting for socio-economic and pregnancy-related confounders.
Results A quadratic relationship between GA at birth and problem behaviour indicates that both preterm and post-term children have higher behavioural and emotional problem scores than the term born children. Compared with term born children, post-term born children had a higher risk for overall problem behaviour [odds ratio (OR) = 2.10, 95% confidence interval (CI) = 1.32–3.36] and were almost two and a half times as likely to have attention deficit / hyperactivity problem behaviour (OR = 2.44, 95% CI = 1.38–4.32).
Conclusions Post-term birth was associated with more behavioural and emotional problems in early childhood, especially attention deficit / hyperactivity problem behaviour. When considering expectant management, this aspect of post-term pregnancy should be taken into account.
Key words : Post-term birth /preterm birth / behavioural and emotional problems / childhood
Introduction
Timely onset of labour is important for peri- and post-natal health. Both preterm (<37 weeks of gestation) and post-term birth (≥42 weeks of gestation) are associated with neonatal morbidity and mortality.1–3 Local management protocols with regard to elective caesarean delivery and labour induction affect the prevalence of post-term birth. Overall, labour induction before or at 42 weeks of gestation has increased,1 but post-term births still occur relatively frequently (up to 5–10%), even in industrialized countries.3,4 Accurate pregnancy dating is critical to the diagnosis of post-term births.3,4 Routine use of ultrasound to confirm pregnancy dating can decrease occurrence of post-term birth.5 Common risk factors for post-term birth include obesity, nulliparity and prior post-term birth and rare causes include placental sulphatase deficiency (an X-linked recessive disorder characterized by low estriol levels), fetal adrenal hypoplasia or insufficiency and trisomy 16 and 18.1,2,6,7
The long-term problems associated with preterm birth, such as increased incidence of cerebral palsy, sensory impairments and behavioural problems are well known.8 The studies investigating effects of post-term birth have focused on the risks during pregnancy and delivery.9 Post-term birth increased the risk of neonatal encephalopathy and death during the first year of life,5,10 but the long-term consequences are unclear. One of the few studies performed found that post-term born infants did not differ from controls at age 2 years regarding general intelligence, physical milestones and illnesses.11 However, a recent study using referral to a neurologist or psychologist as indicator of developmental problems found that 13% of children born post-term had a neurological or developmental disorder at the age of 5 years.12
In this population-based prospective study, we hypothesize that post-term birth is related to behavioural and emotional problems in preschool children. In order to examine the specificity of the association between post-term birth and problem behaviour, we examined specific behavioural and emotional problems including attention deficit / hyperactivity disorder problems (ADHD), affective problems and pervasive developmental problems.
Materials and methods
This study was embedded within the Generation R Study, a population-based cohort from fetal life onwards.13 Briefly, pregnant women who were resident in Rotterdam, The Netherlands, and whose delivery dates were between April 2002 and January 2006, were asked by their midwives and gynaecologists to participate. In the post-natal follow-up of the Generation R cohort, 7484 live born children and their prenatally recruited mothers participated. Post-natally, 38 children died. The remaining 7446 children were eligible for the study. Mothers of 477 children withdrew consent, and mothers of 410 children gave restricted consent (i.e. no participation in questionnaire studies). The remaining mothers of 6559 children gave full consent for post-natal follow-up. We excluded twin pregnancies, leaving 6422 children who could be contacted. Information on child behavioural and emotional problems at 18 and/or 36 months was available for 5145 children (response rate of 78%). Maternal report at both 18 and 36 months was available for 3840 children, 812 mothers reported at 18 months only and 493 mothers reported at 36 months only. The Medical Ethical Review Board of the Erasmus Medical Centre, Rotterdam approved the study protocol. All parents of participating children gave written informed consent.
Ultrasound during the first visit determined gestational age (GA) to the nearest day, which will be expressed in our analyses in weeks. In total, 4132 women (80%) had their first ultrasound examination in early pregnancy (median 13.1 weeks, range 5.1–18.0), 868 women (17%) had it in mid-pregnancy (20.4 weeks, 18.1–25.0) and only 145 women (3%) had their first ultrasound examination in late pregnancy (30.2 weeks, 25.1–39.2). Crown–rump length was used for pregnancy dating until a GA of 12 weeks and 5 days (crown–rump length <65 mm), and biparietal diameter was used for pregnancy dating thereafter (GA from 12 weeks and 5 days onwards, biparietal diameter >23 mm). Methods for establishing GA and standard ultrasound planes for fetal measurements have been described previously.14 Inter- and intra-observer intra-class correlation coefficients were all >0.98.14
Preterm birth was defined as birth before 37 weeks gestation (N = 226) and post-term birth was defined as birth after ≥42 weeks gestation (N = 382). As an additional comparison group, we defined a group of children born before 35 weeks of gestation (N = 78) which is normally included in cohorts of preterm babies.
The Child Behavior Checklist for toddlers (CBCL/1.5–5) was used to obtain standardized parental reports of children’s behavioural and emotional problems.15,16 The CBCL was a postal questionnaire and sent to be filled out by the mother when the child was 18 months old and again when the child was 36 months old. At 36 months of age, we also asked the father to fill out the CBCL. Each item (99 items in total) is scored on a three-point scale (0 = not true, 1 = somewhat or sometimes true and 2 = very true or often true), based on the child’s behaviour during the preceding 2 months. The sum of all problem items is the Total Problems score. There are five Diagnostic and Statistical Manual of Mental Disorders (DSM)-oriented scales: anxiety problems, affective problems, pervasive developmental problems, ADHD and oppositional defiant problems. It has been shown that these DSM-oriented scales provide accurate and supplementary information on clinical diagnoses.17 Also, good reliability and validity have been reported for the CBCL.16 We used the clinical cut-off scores (91st percentile for the Total Problems score and 98th percentile for the syndrome scales) to classify children as having behavioural problems in the clinical range.17 When parents filled out the questionnaire, they were not aware of our research question exploring the relation between post-term birth and behavioural problems, but parents generally are aware of the GA of their child and the risks associated with preterm birth. The maternal CBCL Total Problems ratings at 18 months and 36 months were correlated (r = 0.58, P < 0.001). Maternal and paternal CBCL Total Problems ratings at 36 months were correlated (r = 0.56, P < 0.001).
Several covariates were considered in the analyses and were chosen based on the existing literature and effect estimate changes. Maternal weight and height were measured at intake. We used postal questionnaires to obtain information on mother’s parity, ethnicity and family income. Maternal ethnicity was defined according to the classification of Statistics Netherlands.18 Educational level was categorized into three levels: primary, secondary and higher education.19 Information about maternal smoking and alcohol use was obtained by questionnaires in each trimester. Based on these questionnaires, maternal smoking or drinking were categorized into ‘no’, ‘until pregnancy was known’ and ‘continued during pregnancy’ as described previously.20 The Brief Symptom Inventory (BSI) was used to assess maternal psychopathology in mid-pregnancy; the BSI is a validated self-report questionnaire, which defines a spectrum of psychiatric symptoms.21 Registries provided information on obstetric variables such as induction, birthweight, mode of delivery, umbilical artery pH and Apgar scores after 1 and 5 min. The post-natal questionnaire administered at age 6 and 12 months was used to gather information on breastfeeding and frequency of day care use.
For descriptive analyses, children were categorized in three groups based on GA: (i) born after 37 weeks of gestation up to and including 41 weeks and 6 days (term, reference group); (ii) born after <37 weeks of gestation (preterm); and (iii) born after 42 + 0 weeks of gestation or more
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