AFJOG

African Journal of Obstetrics and Gynaecology | Volume 2 | Issue 3 | 2024 | 25 ORIGINAL RESEARCH African Journal of Obstetrics and Gynaecology | Volume 2 | Issue 3 | 2024 | The role of foot length measurement to determine the gestational age in stillbirths ABSTRACT Background: Women with stillborn infants are often unbooked for antenatal care and are unsure of their last normal menstrual periods. Measuring the neonatal foot length of a stillborn is another possible method for determining the gestational age. Objective: To determine the gestational age from the foot length using the modified Merz model in stillborn infants and to assess the accuracy compared to the gold standard, an early ultrasound (EUS) with gestational age < 24 weeks. Methods: This prospective study was conducted at Kalafong Provincial Tertiary Hospital from 01 August 2017 – 31 August 2018. The foot length was measured using non-stretching tape from the tip of the big toe to the heel of the foot. The Merz chart was used to establish the foot length gestational age. A bland Altman plot was executed, and growth was assessed using the Fenton growth charts. Results: In total, 82 stillborn infants were included. The gestational age was determined by an EUS in 32 cases, sure dates (SD) in 32 cases, and symphysis fundal height (SFH) in 18 cases. The foot length gestational age was highly correlated with the actual gestational age (r=0.908; p < 0.001). The EUS population showed the least percentage of accuracy: 19 (54.3%) cases, SFH with 10 (28.6%) and SD with 6 (17.1%) cases. On average, the foot length gestational age was 1.2 +/- 2.6 weeks less than the EUS gestational age (1.23; 95% CI 0.27 - 2.18; t= 2.6; p = 0.01). The Bland Altman plot for the early sonar population highlighted the inaccuracy between the two methods. The EUS population had more growth-restricted stillbirths (19%). The foot length measurement was limited by the presence of maceration (p = 0.04) and impaired growth. Conclusion: The results suggested that foot length measurement in stillborn infants lacked accuracy in determining the gestational age, especially in the presence of intrauterine growth restriction and maceration. INTRODUCTION According to the World Health Organization (WHO), a stillbirth refers to a baby born with a birth weight of ≥ 1000g or after 28 weeks’ gestation with no signs of life. 1 In South Africa, according to the Birth and Death Registration Act (Act No.51 of 1992), a stillborn refers to a baby born with no signs of life after 26 weeks gestation. 2 In South Africa, all newborns weighing >500g, regardless of the outcome, are counted and regarded as potentially viable. Accurate dating of pregnancy is vital to improve outcomes. The first day of the last normal menstrual period (LNMP) is commonly used to date pregnancy. 3 However, most women are unsure of the starting date of their last menstrual period, have irregular cycles, and may have variable ovulation. 4 In a study by Chiazze et al. of over 30,000 women, only 77% had regular menstrual cycles varying between 25 and 31 days. 3 An additional barrier with this method is that most women are unable to routinely recall their last normal menstruation periods, further limiting its reliability. Symphysis-fundal height (SFH) is another widely used method (measuring the distance in centimetres from the symphysis pubis bone's upper border to the uterine fundus's highest point). The measured height in centimetres corresponds to the gestational age. However, this method is often suboptimal and associated with a wide inter-observer variation. Beazly et al., analysed the accuracy of symphysis fundal height measurement to determine the gestational age, and found a variation of up to eight weeks’ difference from the actual gestational age. 5 An early ultrasound (EUS) before 24 weeks is considered the gold standard to determine the gestational age. 6 During the first trimester, fetal crown-rump length (CRL) is reliable for up to 14 weeks. During the second trimester, measurements include the bi-parietal diameter (BPD), head circumference (HC), abdominal circumference (AC) and femur length (FL). The most common limitation of using ultrasound is the wide inter-observer variability and operator experience. 6,7 Foot length measurement to determine the gestational age was first assessed by Streeter using post-mortem specimens, and his findings have been reproduced in various antenatal and postnatal reports. 8,9 Earlier studies found a correlation between antenatal ultrasound-determined foot length and postnatal foot length measurements. 9 Mercer et al. assessed 223 postpartum and 224 antenatal sonographic foot lengths between 11 and 43 weeks gestation and found that foot length is reliable for determining gestational age. 10 Merz et al. analysed 610 pregnancies with gestational age based on an early ultrasound (< 12 weeks gestation) and found that foot length derived gestational age corresponded to the ultrasound gestational age with high accuracy. 11 They constructed reference ranges for foot length at a specific gestational age. The foot length reference ranges established in the Merz et al. study resemble the anatomic reference range published by Streeter and those developed by Mercer et al. 10 These findings presented reliable reference ranges for the foot length to establish the gestational age. Hirst et al. found a high linear correlation between the actual gestational age and the foot length gestational age in stillbirths.10 Equally, Maroun et al. and Ho et al. found a high correlation between foot length and actual gestational age. 13,14 Foot length measurement is simple, inexpensive, DN Emvula 1 , J Makin 2,3 , FM Molokoane 1,2,3 1 Department of Obstetrics and Gynaecology, University of Pretoria 2 South African Medical Research Council, University of Pretoria 3 Maternal and Infant Health Care Strategies Unit, University of Pretoria CORRESPONDENCE: DN Emvula | Email: david.emvula@yahoo.com The role of foot length measurement to determine the gestational age in stillbirths