Background
Prevalence of gestational diabetes mellitus (GDM) is increasing. Globally, around 76 million women of reproductive age are either suffering from impaired glucose tolerance (IGT) or diabetes in pregnancy (DIP)[1]. Dysglycemia during pregnancy is known to cause fetal macrosomia or dysmaturity[2]. The accurate knowledge of fetal gestational age (FGA) is a keystone in decision-making regarding the optimal timing of delivery in diabetes in pregnancies. About 10% - 45% of the women do not know their last menstrual period (LMP) and at times they first attend the antenatal clinics in their last trimester of pregnancy [3]. This may result in iatrogenic premature births, leading to increased perinatal morbidity and mortality. There are many ultrasonic parameters to determine FGA, but the most accurate one is the measurement of Transcerebeller Diameter (TCD) which correlates well in predicting FGA.

Aim
To determine the predictability of fetal gestational age (FGA) by sonographic measurement of TCD in pregnancy with diabetes during third trimester.

Method
A case-control study was planned to know whether fetal sonographic TCD in pregnancy with diabetes can predicts the actual GA as in normal pregnancies.

The study period was from August 2016 – June 2017, conducted in the Tanveer Ultrasound Clinic, Karachi-Pakistan. Ethical approval was obtained from ERB of Fatimabai Hospital, Karachi and informed consent was obtained from women. A non-probability consecutive sampling method was used to select 179 women in their third trimester of pregnancy; 92 with DIP and 87 normal pregnancies that were sure of their LMP and had regular periods for the last six months. Women were matched for parity, body weight and age. The senior sonologists were trained in calculating TCDs. Women who were not sure of their LMP and had obstetrical co--morbidities other than diabetes were excluded from the study.

Results
The average age of the women was 26.48±12 years and mean parity was 5.2±0.5. The mean fetal TCD at 28-42 weeks was 33.5±3.06 mm in both study groups. After applying ANOVA test on parity, GA and maternal age (MA) revealed that GA and TCD (mm) were significantly correlated (p=0.002) as compared to other fetal biometric measurements like biparietal diameter, femur length, and abdominal circumference in both the groups.

Gestation Period (GA in weeks)	DIP (n)	Normal (n)	TCD±SD (mm)	p-value
28-32	27	41	26±5.36	0.0001
32-36	21	18	28±3.83	0.0005
36-40	30	13	34±0.39	0.0008
40-42	10	13	36±1.78	0.0004
42+	4	2	38±3.15	0.0002
Total	92	87	39±3.82	0.002
 	 	Average TCD±SD	33.5±3.06	 
Discussion
The measurement of TCD in the fetus is a useful indicator for gestational age even in the presence of dysmaturity and macrosomia. The analysis shows that the fetal TCD’s in DIP corresponds to the fetal gestational age in a similar fashion as in normal pregnancies and seems to be more predictive of gestational age as compared to other fetal parameters. Montenegro [4] also stated that TCD seems to be good marker for gestational age compared to other clinical and biometric parameters. Similar results were obtained by Strizhova [5].

References:

Federation, I.D., 2015. IDF Diabetes Atlas 6th.

Kc, K., Shakya, S. and Zhang, H., 2015. Gestational diabetes mellitus and macrosomia: a literature review. Annals of Nutrition and Metabolism, 66(Suppl. 2), pp.14-20.

Ugwu, E.O., Odoh, G.U., Dim, C.C., Obi, S.N., Ezugwu, E.C. and Okafor, I.I., 2014. Women’s perception of accuracy of ultrasound dating in late pregnancy: a challenge to prevention of prolonged pregnancy in a resource-poor nigerian setting. International journal of women's health, 6, p.195.

Monotenegro NA, Leite LP. Fetal cerebellar measurements in second trimester ultrasonography-clinical value. J Perinat Med 1989;17:365-9.

Conflict of Interest:
I have no potential conflict of interest to disclose

Fetal transcerebellar diameter measurement for prediction of gestational age in 3rd trimester of pregnancy with diabetes