The study was conducted at the Department of Obstetrics and Gynaecology, University of Abuja Teaching Hospital, Abuja, Nigeria, a 350-bed tertiary health facility. In this facility, modified biophysical profile is used to monitor postdate pregnancy. The major limitation is cardiotocography is not done due to unavailability of a functioning machine. With the availability of a modern ultrasound machine with a Doppler facility, a Doppler scan may be worthwhile in management of the postdate pregnancies.
This was a prospective observational study of women with uncomplicated postdate pregnancies at gestational age of 40–41+ 3 weeks, from August 2018-Febuary 2019. Women with singletons live fetus in cephalic presentation and accurate dating were included in the study. Women with the following were excluded; obstetric or medical complication(s) - IUGR, diabetes mellitus, hypertensive diseases in pregnancy, sickles cell disease, poor dating, multiple pregnancy, and breech presentation. A calculated sample size of 100 using: A calculated sample size of 100 (using n = z2pq/d2, where n is sample size, z is standard normal deviation (a constant) where n is sample size, z is standard normal deviation (a constant) which is 1.96 at 95% confidence interval at 95% confidence interval, p is percentage of study population with abnormal CPR from a previous study, q is 1-p and d is margin of error of 5%, and attrition of 10%) was used. An informed consent was obtained from each woman before inclusion in the study.
At the time of the study, there was no facility for fetal blood sampling and measurement of blood gases to confirm fetal distress. Use of cardiotocography (CTG) was not possible due to a faulty CTG machine.
Consent to participate were written and also verbally reaffirmed by the participants. After obtaining consent from the participants, the ultrasound was carried out using the General Electric Healthcare Voluson™ P8 (2016 model) with Doppler unit and convex linear transducer 3.5 MHz. A basic scan was first conducted in B - Mode using the 3.5 MHz curvilinear transducer to determine the viability, number, lie and presentation of the fetus as well as the placentation and liquor volume. A fetal biometry was carried out.
Using the same transducer and mode, a free loop of umbilical cord was located. The umbilical artery was identified using colour Doppler interrogation. Pulsed Doppler with a gate size of 2 mm was applied at an angle of insolation ≤ 30°. The pulsatility index (PI) was automatically generated by the machine and value recorded when uniform consecutive waveforms were generated in the absence of fetal movement and breathing.
Pulsatility Index (PI) = Peak systolic flow – end diastolic flow 𝑚𝑒𝑎𝑛𝑓𝑙𝑜𝑤
Middle cerebral artery (MCA) Axial section of the brain, including the thalami and septum cavum pellucidi was obtained and magnified on B-Mode. Traducer was moved to the base of the skull until the circle of Willis was identified. The MCA was identified with colour Doppler. The scanning plane was adjusted to obtain an insonation angle close to 0° but < 15° at the level of the proximal portion of the MCA close to its origin from the circle of Willis with a sample volume of 2–3 mm. Care was taken not to exert pressure on the fetal head because this alters the flow velocity waveforms from the MCA. The automatically generated pulsatility index (PI) was recorded when uniform consecutive waveforms were generated in the absence of fetal movement and breathing. The right and left MCA pulsatility index was measured, and the mean recorded. The pulsatility index (PI) and the cerebroplacental ratio was calculated using the formula:
Pulsatility Index (PI): Peak systolic flow – end diastolic flow 𝑚𝑒𝑎𝑛𝑓𝑙𝑜𝑤
Cerebroplacental ratio (CPR) = Middle Cerebral Artery-PI/Umbilical Artery -PI
The Doppler evaluation was done once by the researcher and the consultant radiologist. Patients were followed up till delivery and relevant data collected. Cutoff values for normal and abnormal UA PI, MCAPI and CPR were generated using the 10th and 90th percentile. The study population was divided into two groups based on normal and abnormal Doppler parameters.
Adverse perinatal outcome was defined as the presence of one or more of the following: Fetal distress, Apgar score < 7 at 1 and 5 min, meconium aspiration syndrome (MAS) and admission into Special care baby unit (SCBU).
Data was entered into a personal computer and analysis was done using the IBM Statistical Package for the Social Sciences (SPSS) version 23 software. A percentile plot of the Doppler variables was carried out and the UA PI was considered abnormal when the values were > 90th percentile while the MCA PI and CPR were considered abnormal when the values were < 10th percentile. Chi square was used for categorical variables and where the criterion for X2- test was not met, Fisher’s Exact Test was used.
Primary outcome measures were fetal distress and birth asphyxia. Secondary outcome measures were: MAS, admission into SCBU, CS for fetal distress, PPH. MAS were diagnosed as visual observation of greenish discoloration of the liquor with respiratory difficulties. Fetal distress was defined as ominous FHR changes (tachycardia or bradycardia) that led to caesarean section or instrumental delivery.
Approval for the conduct of the study was obtained from the Health Research and Ethics Committee of University of Abuja Teaching Hospital.