Prevalence and factors associated with preterm birth at kenyatta national hospital

A hospital based descriptive cross-sectional study was conducted using interviewer administered questionnaire. Additional information was obtained from medical records of the mothers and babies.

KNH is the largest referral hospital in Kenya and Eastern and Central Africa and also serves as a teaching hospital for the University of Nairobi and the Kenya Medical Training College. It is located in Nairobi which is the capital city of Kenya with a population of about 4 million. The hospital has a busy maternity unit registering over 10,000 deliveries annually. It also has a busy newborn unit (NBU) which offers specialised neonatal care. Being a teaching and referral hospital, KNH handles many high risk pregnancies whose outcomes often include preterm birth.

The study population comprised of all mothers who had live births at Kenyatta National Hospital and their newborns. A total of 322 mothers who met the eligibility criteria were enrolled into the study. These mothers delivered a total of 331 babies 18 of which were twins.

All mothers who had live births at KNH in December 2013 were identified using the birth register within 24 h of delivery. Systematic sampling was used to recruit mother-baby pairs. Mothers were traced to the postnatal wards. Informed consent was obtained from the mothers and babies admitted to the newborn unit were also traced. A standard pretested questionnaire was administered to the mothers while additional data was obtained from the mothers’ and babies’ medical records as required. The records examined for additional data included the mothers’ antenatal and admission records and the babies’ medical records for those admitted in the NBU after delivery. Information collected from the mother included maternal age, marital status, level of education, occupation, smoking and alcohol use during pregnancy, parity, date of last normal menstrual period, date of current and preceding delivery (for calculation of interpregnancy interval) and history of previous preterm birth. Information obtained from medical records included antenatal clinic (ANC) attendance and number of visits, Human Immune Deficiency (HIV) status, hemoglobin level, mode of delivery, onset of labor (spontaneous or medically indicated), pregnancy outcome (singleton or multiple), birthweight (to nearest 10 g), baby’s gender, prelabor rupture of membranes (PROM) for > 18 h, pregnancy induced hypertension (PIH), antepartum hemorrhage (APH), history of burning sensation during pregnancy or treatment for urinary tract infection (UTI). Anemia was defined as hemoglobin level of < 10 g/dl. PIH was defined clinically as a blood pressure of > 140/90 mmHg after 20 weeks of gestation with or without proteinuria and/or edema as diagnosed and documented by the attending clinician. APH was defined as any vaginal bleeding in the mother after 24 weeks of gestation as documented in the records by the attending clinician. UTI was defined as a documented clinical/laboratory diagnosis of UTI any time during the pregnancy and/or a positive history of treatment of burning sensation with micturition as reported by the mother. Maternal nutritional status was assessed by measuring the left mid-upper arm circumference (MUAC) using non-stretchable World Food Program MUAC tapes used for screening pregnant mothers. A low MUAC was defined as a measurement of less than 24 cm. Gestational age was calculated using a standard obstetric wheel based on menstrual dates and confirmed within 24 h of birth by clinical assessment using the Finnstrom Score. This method was developed by Finnstrom et al. in 1977. Seven (7) physical parameters which are scalp hair, skin opacity, length of fingernails, breast size, nipple formation, ear cartilage and plantar skin creases were used. This tool is not only easy to use but is also sensitive with an accuracy of +/− 2 weeks when administered within 24 h of birth [8, 9]. To limit observer bias, gestational assessment of all babies was done by only one research assistant trained by the principal investigator and aided by a printed pictorial scoring chart. For uniformity, gestational age used for analysis was based on Finnstrom score and not on menstrual dates. Preterm birth was defined as a gestation of less than 37 completed weeks. Prematurity was further categorized as extreme (less than 28 weeks), severe (28–31 weeks), moderate (32–33 weeks) and late preterm or near term (34–36 weeks).

Data was entered into Microsoft Access database, cleaned and stored in a password protected external storage device. Data was analyzed using Stata 11.0. Mean, median, frequencies and percentages were reported to describe the variables and inferential statistics were used to establish associations between prematurity and the various risk factors using a chi-square analysis. Multivariate logistic regression was used to determine the factors independently associated with preterm birth.

The mean maternal age was 26 ± 5 years with majority (89%) being aged 20 years and above. Most of the mothers (83%) were married. About 85% of the mothers had attained post-primary level of education. About 97% of the enrolled mothers had singleton deliveries while 82% delivered at term. Fifty three percent of all the babies in the study were males. The mean birth weight of term babies was 3059 ± 538 g. The median weight of preterm babies was 2110 g (IQR 1650–2400). The mean gestation was 39 ± 3 weeks and 33 ± 3 weeks for term and preterm babies respectively. Of the preterm births, 62% were late preterms (34–36 weeks), 19% were moderate preterms (32-33 weeks), 16% were severe preterm (28–31 weeks) and 3% were extreme preterm (< 28 weeks).

The prevalence of preterm birth among live births was 18.3% (95% Confidence Interval (CI) of 14.1–22.5%).

About 80% of mothers in the term and 90% in the preterm group were aged 20–34 years. Thirteen percent of mothers aged less than 20 years delivered at term compared to 3.4% who had preterm delivery and this was significant (p = 0.034). The proportions of mothers aged 35 years and above were similar in the two groups. There was no difference between the preterm and term groups in terms of marital status (p = 0.133), maternal level of education (p = 0.330), occupation (p = 0.823), smoking (p = 0.728), antenatal alcohol use (p = 0.501) and maternal MUAC (p = 0.651). None of the socio-demographic factors was significantly associated with preterm birth except maternal age less than 20 years which was negatively associated with preterm delivery (OR 0.236). Table 1 shows the relationship between the socio-demographic characteristics and preterm delivery.

Most mothers had a parity of less than four. Women with a parity of 4 or more were nearly 5 times more likely to deliver preterm compared to those whose parity was < 4 (p = 0.019; OR 4.709). About 35% of mothers who delivered before term had a history of previous preterm delivery compared to 16% of those who delivered at term and this was significant (p = 0.010). Approximately 6% of mothers in the preterm group and 11% in the term group had an interpregnancy interval of < 24 months but this was not statistically significant (p = 0.357)). The relationship between previous pregnancy characteristics and preterm birth is summarized in Table 2.

The proportion of mothers who did not attend ANC in the term and preterm groups was 2.3 and 3.4% respectively and this was not significant (p = 0.621). Mothers who had not had any antenatal care were one and a half times more likely to deliver preterm (OR 1.503). About 29% of mothers in term and 37% in preterm group had less than 3 antenatal visits but this was statistically insignificant (p = 0.256). Approximately 13% of preterm mothers and 12% of term mothers were HIV positive. There was no association between HIV status and preterm delivery (p = 0.834). The proportion of women who had anemia during pregnancy was the same for the two groups (p = 0886). Table 3 shows the relationship between the antenatal characteristics and preterm delivery.

Approximately 40% of preterm deliveries were via Caesarean section (C/S) compared to 26% among those who delivered vaginally. Women who delivered via Caesarean section were nearly two times (OR 1.832) more likely to deliver preterm than those who delivered vaginally. Delivery via Caesarean section had significant but marginal association with preterm birth (p = 0.049). About 28 and 36% of mothers in the term and preterm group respectively had induced labor or medically indicated C/S. However, there was no association between onset of labour and preterm birth (p = 0.231). The proportion of twin pregnancy among women who delivered at term and preterm was 2 and 7% respectively and this was significant (p = 0.040). Twin pregnancy conferred nearly a 4-fold increase in the risk of preterm birth (OR 3.753). Table 4 shows the relationship between the delivery characteristics and preterm delivery.

About 32 and 8% of mothers in the preterm and term groups had PIH while 13 and 5% of mothers in the two groups had APH respectively. Mothers with PIH and those with APH had a 5-fold and 3-fold increase in risk of preterm birth (OR 5.203 and 2.790). Approximately 27% of mothers who had preterm delivery and 8% of those who delivered at term had a history of PROM for more than 18 h while 47.5% of mothers in preterm group and 32% of those in the term group respectively reported having had UTI or burning sensation with micturition during pregnancy. As shown in Table 5, all these factors were significantly associated with preterm birth (p < 0.05).

Maternal age, parity, previous preterm birth, twin gestation, UTI, PIH, prolonged PROM and APH were found to be significantly associated with preterm birth. However, on multivariate logistic regression only PIH, APH and prolonged PROM remained significant. The risk of preterm birth increased 8-fold with PIH (OR 7.805), 5-fold if the mother had prolonged PROM (OR 5.319) and 4-fold with APH (OR 4.264) after controlling for confounders. The multivariate logistic regression is summarized in Table 6.

Only mothers who had live births were interviewed and their babies assessed for gestational age. The study did not address factors associated with preterm stillbirth. UTI in pregnancy was partly based on mothers’ self report of symptoms and not on laboratory confirmation and therefore over-reporting was likely. Clinical assessment of gestation using the Finnstrom method that solely relied on physical characteristics is also a limitation of this study. Use of secondary data for some variables is another limitation of our study.