Annals of African Medicine, Vol. 3, No. 3, 2004, pp. 126-129

HEAD CIRCUMFERENCE AT TIME OF BIRTH: A POSSIBLE PREDICTOR OF LABOUR OUTCOME IN SINGLETON CEPHALIC DELIVERIES AT TERM?

O. A. Ayinde and A. O. Omigbodun

Department of Obstetrics and Gynaecology, University College Hospital, Ibadan, Nigeria
Reprint requests to: Dr. O.A Ayinde, Department of Obstetrics and Gynaecology, University College Hospital, Ibadan, Nigeria. E-mail: sola_ayinde@yahoo.com

Code Number: am04031

ABSTRACT

Background: Several studies have attempted to predict the outcome of labour in cephalic presentation using such parameters as maternal pelvic dimensions and estimated fetal weight. Though, the fetal head is widely recognised as the best ‘pelvimeter’, dimensions of the fetal head have been neglected for this purpose. The study was therefore aimed at determining any possible association between fetal head circumference at the time of birth and the route of delivery in parturient women.
Method: Hospital records of all term singleton cephalic deliveries between January and December 1999 at the University College Hospital, Ibadan were examined.  Maternal characteristics such as age, parity and fetal characteristics such as gestational age at delivery, birth weight, Apgar scores and sex were recorded. The occipito-frontal circumference was measured in centimetres  on the second day of life when caput and moulding would have subsided by the attending paediatric resident doctor as part of routine examination of the newborn. Relationship between head circumference and mode of delivery was studied by comparing women who had vaginal delivery with those who had caesarean section on account of dystocia in labour.
Results: While there was  no significant difference in caeserean section rate in the the parous women, the rate in nullipara rose markedly from 13.3% with fetal head circumference of less than 37cm to 60.0% for measurements of 37cm and above.
Conclusion: Fetal head circumference may be useful in predicting the likely mode of delivery especially in the nullipara. Prospective studies using ultrasonically determined fetal head circumference at the time of labour are recommended to further substantiate the findings.

Key words: Head circumference, labour outcome, singleton cephalic delivery, term

INTRODUCTION

Mechanics of labour depends on three interacting factors. These are ‘power’, “passenger’ and ‘passage’. ¹ Power is the strength of uterine contractions. The progress of labour partly depends on this factor which causes progressive effacement and dilatation of the cervix and descent of the fetus. ^{2 The} ‘passenger’ is the fetus while the passage refers to the maternal pelvis. Fetal morphology, dimensions and weight are all known to influence the outcome of labour. Extremes of birth weights and structural abnormalities are associated with poor progress in labour.  ^{3, 4}

The maternal pelvis must be adequate for fetal size to enable the latter to pass through the birth canal. This informs the wide usage of pelvimetry in predicting the outcome of labour for a long time.  ^{5, 6} In cephalic presentation the size of the fetal head largely determines the ease with which parturition occurs. ³ In spite of this, not much work has been done in the area of attempting to predict labour outcome using dimensions of the fetal head. This study was aimed at determining whether fetal head circumference at the time of birth has a relationship with the mode of delivery in parturient women.

MATERIAL AND METHODS

Hospital records of all term singleton cephalic deliveries between January and December 1999 at the University College Hospital, Ibadan were examined. Maternal characteristics such as age, parity and fetal characteristics such as gestational age at delivery, birth weight, Apgar scores and sex were all recorded. The occipito-frontal circumference was measured in centimeters (one decimal place) on the second day of life when caput and moulding would have subsided by the attending paediatric resident doctor, as part of routine examination of the newborn. Effect of head circumference on mode of delivery was studied by comparing women who had vaginal delivery with those who had caesarean section.

The women included in the study were only those who had normal singleton pregnancies, cephalic presentation in labour and were delivered either vaginally or by emergency caesarean operation for unsatisfactory progress or dystocia (inspite of adequacy of uterine contractions which was ensured by oxytocin augmentation as necessary). All labours were monitored with the partograph. Women with uncertain gestational age, intrauterine fetal deaths and fetal anomalies were excluded. Those who had elective or emergency caesarean section for indications such as antepartum haemorrhage, preeclampsia/ eclampsia, poorly controlled diabetes mellitus and other medical disorders of pregnancy prior to onset of labour were also excluded.

Observed differences were subjected to statistical tests for significance at p value < 0.05. Chi-square test was used to compare discrete variables while Student’s t-test was used for continuous variables as appropriate. The relationship between two continuous variables was measured with Pearson correlation coefficient (r). EPI Info 2000 statistical package was used for data entry and analysis.

RESULTS

Three hundred and thirty nine patients who met the inclusion criteria were recruited for the study. The age range of the women studied was 17 to 44 years while the mean was 29.6 years (±4.6 years). The mean parity was 2.29 (range: 0 to 6). The mean values and standard deviations (in parenthesis) of other birth variables, namely, head circumference, birth weight, gestational age and duration of labour were 34.8cm (±1.3cm), 3.2kg (± 0.6kg), , 39.5 weeks (±1.4 weeks) and 7.8 hours (±4.2 hours) respectively. The mean durations of labour in the nulliparous and parous women were 10.8 hours (s.d.:4.7 hours) and 6.2 hours (s.d.:3.5 hours) respectively (t=5.23, p

Table 1 shows the clinical characteristics of study subjects based on the mode of delivery. The mean birth weight, gestational age at birth and head circumference in women who had caesarean delivery was significantly higher than the values in those who achieved vaginal delivery. The mean Apgar scores were lower in the caesarean section group, though, only the 5 minute score was significantly lower(p=0.019). While there was no significant difference in caesarean section rate in the parous women, the rate in nullipara rose markedly with fetal head circumference of 37cm and above (table 2). The need for abdominal delivery was significantly more for babies with head circumference of 37cm and above (x² =25.6, df=l, pFigure 1 further illustrates this. In table 3, there was a gradual but consistent increase in birth weight with increasing head circumference (r=O.1 85, p

Table 1: Clinical characteristics of study subjects

GA= Gestational age; BW= Birth weight; HC= Head circumference; AS¹=Apgar score at 1 minute; AS⁵=Apgar score at 5 minutes; Sd =Standard deviation

Table 2: Head circumference and mode of delivery

VD= Vaginal delivery; CS= Caesarean section

Table 3: Relationship between head circumference, gestational age and birth weight

DISCUSSION

The study investigated the likely association between head circumference at birth and the mode of delivery. It was shown that there was no significant relationship between head circumference and route of delivery in parous women. However, in nullipara, vaginal delivery was more frequently achieved when fetal head circumference at birth was below 37cm. This appears to be the critical head circumference in the determination of mode of delivery.

The mean head circumference of 34.8cm in this study falls within the normal range of head circumference for fetuses at term earlier reported inthis environment. ⁷ The mean head circumference in male newborns was significantly greater than for females. This observation was similar to the findings in previous studies by Megafu et al and Fasubaa et al. ^{8, 9} The mean birth weight of 3.2kg also compares with 3.4kg reported in earlier study by Adinma and Agbai. ³ Also, the mean duration of labour of 7.8 hours found in this study compares with what was reported in the same study. Duration of labour was however significantly shorter in parous women than in their nulliparous counterparts.

Overall, this study has suggested that fetal head circumference has a role to play in the determination of the route of delivery, especially in the nullipara. The fetal head circumference used in the study was however measured after birth. We therefore recommend that prospective studies using ultrasonically determined fetal head circumference at the time of labour would be needed to further substantiate the findings.

REFERENCES