Comparison of diagnostic value of two-dimensional ultrasound and clinical examination in fetal weight estimation.

Background: Estimation of fetal weight during pregnancy plays an important role in prenatal and intrapartum care and is more important in pregnancies after 37 weeks to determine the type of delivery. The aim of this study was to compare and evaluate the accuracy and diagnostic value of two-dimensional ultrasound and clinical examination in estimating fetal weight and pregnancy outcomes. Materials and
Methods: This cross-sectional study was conducted on 300 pregnant women without abnormal fetuses and pregnancies after 37 weeks; mothers who had a normal delivery or cesarean section were evaluated by the available method. The weight of the fetus was estimated before and after delivery, using ultrasound and clinical examination. Newborns were classified into five groups based on their fetal weight. Analysis of collected data was performed with SPSS software.
Results: The mean age of the patients was 31 years and the mean weight of the neonates was 3450 g. At a weight of less than 3000 g, ultrasound and clinical evaluation were strongly correlated with the actual weight of the infant, but at weights of more than 3500 and 4000 g, weight estimation with ultrasound was highly accurate, and clinical examination had poor accuracy. In lower weights, square errors were fewer in both ultrasound and clinical examination, in comparison with higher weights. In higher weights, ultrasound is more reliable, and the diagnostic accuracy of clinical examination is reduced.
Conclusion: Estimation of fetal weight with prenatal ultrasound is highly accurate. Clinical examination is more accurate in determining the weight of small fetuses and does not pay much attention to the diagnosis of macrosomic fetuses and even leads to overestimation, while ultrasound is much more accurate in diagnosing fetal macrosomia. Copyright:

Introduction

The weight of the fetus during pregnancy plays an important role in prenatal care and delivery, and it is more important for determining the type of delivery. Fetal growth retardation increases fetal risks, and fetal macrosomia increases birth trauma, such as shoulder dystocia and damage to the brachial plexus, and the risk of postpartum hemorrhage and birth canal injury. It is also important to diagnose fetuses with intrauterine growth restriction to determine the intervals between prenatal care.[12]

Conducting a study that can provide a simple and reliable estimate of fetal weight can effectively reduce maternal and neonatal complications because prolonging the labor process may lead to surgical or obstetric interventions, which may increase the mortality and morbidity, and the costs of treatment. Surgical delivery and fetal macrosomia are associated with a 3- to 5-fold increase in pelvic floor trauma.[34] Pelvic floor trauma during vaginal delivery causes pelvic floor diseases such as urinary stress incontinence and pelvic organ prolapse.[56] Therefore, with the help of ultrasound or clinical examination, many physicians can choose the best method of delivery and minimize the error rate.[7]

In the United States, one-third of all deliveries were performed by cesarean section in 2009, which is a high rate.[8] Since 1996, the prevalence of cesarean delivery in all age groups of mothers has increased by more than 50%.[9] About half of which were related to primary cesarean section. Recent findings show that the Middle East has the highest rate of cesarean section in the world and the statistics are increasing, and it is important to provide diagnostic solutions to reduce cesarean section.[10] Ultrasound is a simple and accessible method that uses the Hadlock formula and fetal biometric parameters including femur length, fetal head circumference, and abdominal circumference.[1112] If ultrasound is not available, fetal weight can be estimated by clinical examination and Leopold maneuvers, as well as by fundus height.

The aim of this study was to compare and evaluate the accuracy and diagnostic value of two-dimensional ultrasound and clinical examination in estimating fetal weight and pregnancy outcomes.

Material and Methods

Study design

The present study is a cross-sectional study, conducted on 300 pregnant mothers with singleton pregnancies without abnormal fetuses and pregnancies after 37 weeks (42–37), who referred to the gynecology department of Dr. Shariati Hospital for normal delivery or cesarean section, in 2018 and 2019. Mothers with abnormal fetuses, fetal breech, or transverse fetuses, patients who referred in the active phase and had dilatations greater than 4 cm, were excluded from the study.

Inclusion and exclusion criteria

Inclusion criteria included women in the age range of 18–42 years, singleton pregnancy, without chronic hypertension, and history of thrombophilia. Exclusion criteria included women with a history of chronic hypertension, smoking or drug abuse, overt or gestational diabetes, kidney disease, megaloblastic anemia, seizure, prior significant illness, personal or familial history of deep vein thrombosis, and/or vitamin deficiency, as well as those receiving any antifolate drugs (antiepileptics, methotrexate).

Method description and data collection

Prior to ultrasound, after emptying the mother’s bladder, fetal weight was estimated by a gynecologist from the abdomen by two-handed examination. The mother was in the supine position, and after straightening her legs, her abdomen was placed between her hands from the top of the symphysis to the pedal between her hands. In patients with fat abdomen, the skin was gently stretched to access the fundus, and if the uterus was placed flat, there is the possibility that the fetus had been pulled around the mother’s pelvis; therefore, the fetus should be slowly moved from the perimeter to the middle of the abdomen for estimation of the correct weight.

Fetal weight was estimated in the ultrasound room, and the method of estimating fetal weight was performed by a professor of perinatology using the Hadlock formula and fetal parameters of biparietal diameter and head circumference, femur length, and abdomen circumference. The physicians who performed clinical and ultrasound assessments were blind to each other.

Then, after normal delivery or cesarean section, the fetal weight was recorded in the neonatal ward immediately after birth (first hour after birth) and after initial cleaning and before breastfeeding or feeding of the infant by the neonatal nurse.

In this study, infant weighs less than 2500 g were considered in the FGR range, 2500–3999 g in the normal range, and weights more than 3999 g were considered fetal macrosomia. Data were collected in a preprepared checklist and analyzed at the end of the research. The study was registered in the Iranian Registry of Clinical Trials IR.TUMS.MEDICINE.REC.1397.536 after approval of the research and ethics committees at the university.

Statistical analysis

The collected information was descriptive (mean, standard deviation, and frequency distribution) and analyzed using pair t-test, C-2 test, and Pearson correlation coefficient. Statistical analysis of data was performed through SPSS 20 software. P values less than 5% were considered as a significant level.

Results

This study was conducted on 300 pregnant women without abnormal fetuses and pregnancies after 37 weeks, and 107 of which were primiparous women (35.6%) and 193 were multiparous women (64.3%) [Table 1]. The youngest patient was 18 years old and the oldest was 40 years old. The mean age was 31 years and the mean gestational age was 38 weeks; most patients were overweight, and only 21.1% had normal body mass index (BMI). The mean weight of the neonates was 3450 g.

Table 1

Demographic data and parity

Parameters	Mean ±, % (n=300)
Age (year)	31.02±3.25
BMI (kg)	26.96±4.10
Gestational age (week)	38.18±1.31
normal BMI	21.1%
weight of the neonates (gr)	3450
Parity group
Primipara	35.6%
Multi Para	64.3%

As can be seen in Table 2, at a weight of less than 3000 g, ultrasound and clinical evaluation have a strong correlation with the actual weight of the baby (P < 0.05), but at a weight of more than 3500 and more than 4000 g, this relationship is strong in ultrasound and high sonography accuracy (P > 0.05).

Table 2

Range of fetal weight (g) in groups

Range of fetal weight (g)	US FEW	P	Clinical FEW	P	ABW
2000-2499	30 (10%)	0.01	28 (9.3%)	0.02	32 (10.6%)
2500-2999	35 (11.6%)	0.03	34 (11.3%)	0.02	32 (10.6%)
3000-3499	92 (30.6%)	0.008	110 (36.6%)	0.09	90 (30%)
3500-3999	101 (33.6%) 88	0.02	68 (22.6%)	0.11	106 (35.3%)
>4000	42 (14.%)	0.01	60 (20%)	0.23	49 (16.3%)
Total	300 (100%)	-	300 (100%)	-	300 (100%)

The results of Table 3 demonstrated that the mean fetal weight was significantly lower in primipara pregnant women than in multipara patients (P < 0.01).

Table 3

Comparison of mean fetal weights between parity groups

Parity Group	Mean fetal weight (g) ± SD	Comparison of mean weight between parity group	P
Primipara	3100±50	Multipara Versus Primipara	0.0001
Multipara	3450±40

It has been observed that maternal body mass and gestational age affect weight estimation in both methods, and the greater the gestational age and BMI, the deeper the effect. Linear regression analysis shows that maternal BMI affects the accuracy of the results so that as maternal weight increases, the rate of diagnostic error increases in both methods. In obese mothers, the weight estimated by ultrasound is even lower than the weight estimated by clinical examination (P < 0.05). [Table 4].

Table 4

Clinical examination in groups. Normal weight=18.5 < BMI <24.99. Overweight=25.0< BMI <29.99. Obesity class I=30.0

Parameters	n (%)	Mean±SD	US/Accuracy (%)	Clinical/Accuracy (%)	All. Accuracy (%)	P
Age
18-30 years old	128 (41)	27.17±2.94	79	69	74	0.036
Above 30 years old	171 (59)	35.84±7.25	21	31	26	0.268
BMI
37-39 week	134 (43)	37.17±2.94	62	59	60.5	0.039
40-42 week	166 (56)	40.84±0.82	38	41	39.5	0.182
BMI
Normal weight	65 (21.6)	22.5±7.19	42	36	39	0.039
Overweight	112 (37.3)	27.7±4.23	32	30	31	0.082
Obesity class I	98 (32.6)	32.2±5.11	16	23	19.5	0.119
Obesity class II	25 (8.3)	36.5±2.84	10	13	11.5	0.182

According to the results of Table 5, the negative predictive value of the clinical examination is high, meaning that if the clinical examination shows that the fetus is not macrosomic, it can be trusted with a 73% probability of correctness, so if the clinical examination states that the fetus is not FGR, it is equally acceptable, while the opposite is not true, so its sensitivity and positive predictive value are low. On the other hand, the results on ultrasound show high sensitivity and specificity and a high positive and negative predictive value.

Table 5

Sensitivity, specificity, PPV, and NPV for each method

Method	Sensitivity	Specificity	PPV	NPV
Ultrasound	68.00	90.88	89.53	86.78
Clinical	50.2	73.23	51.32	73.32
P	0.04	0.03	0.03	0.04

Discussion

Assessing and estimating fetal weight before delivery is one of the prerequisites for pregnancy care in order to reduce maternal and fetal risks and complications. In this study, two-dimensional ultrasound was compared with clinical examination in estimating fetal weight in the third trimester of pregnancy. The weight of the fetus estimated by ultrasound and clinical examination corresponded to the actual weight of the infant after birth. This result was consistent with studies by Lee and Wu in 2020.[1314]

Our study showed that in the weight range of 200–2499 and 2500–2999 g, clinical ultrasound and clinical estimation both had sufficient accuracy in estimation of fetal weight, but at higher weights, ultrasound was more accurate in estimating fetal weight. This indicates the high accuracy of fetal weight estimation by ultrasound, and this finding is consistent with the results of previous studies.[141516]

In our study in lower weights, the square error is lower in both the methods of ultrasound and clinical examination, in comparison with higher weights; on the other hand, in higher weights, ultrasound is more reliable, and the diagnostic accuracy of clinical examination is reduced. It is important to note that in the estimation of higher weights, clinical examination is more unrealistic than the actual weight and the weight estimated by ultrasound, while the clinical examination is reliable in assessing the weight of smaller fetuses and its diagnostic accuracy is higher than ultrasound. These findings support the claim that fetal weight estimation with ultrasound can be highly accurate in diagnosing fetal macrosomia or growth retardation. This finding is consistent with the studies by Streicher et al. (2001) and Murphy et al. (2001) in examining the accuracy and precision of ultrasound and estimating the weight of infants in the range of 500–5000 g.[1718] Findings from other studies also showed similar results.[1920] Ultrasound is more accurate in diagnosing lower weights, although there was no significant difference between the weight estimated by ultrasound and the actual weight in macrosomic fetuses; also, other studies in this field confirmed this finding.[2122] A 2014 study by Goetzinger et al.[23] compared the baby’s actual weight and the weight estimated by clinical examination, which was performed by professors; this study found that professors made about 500 g of error in estimating weight, and the diagnostic accuracy did not increase despite the high experience.

In general, the results of this study showed that estimating fetal weight with prenatal ultrasound is highly accurate, and this method is also highly accurate in diagnosing fetal macrosomia and growth retardation. Clinical examination is also useful for estimation of lower weight, but it is not very accurate in estimation of heavier weights and even leads to overestimation, while ultrasound is very accurate in estimation of heavier weights.

One of the strengths of the study was the appropriate number of the study population. The practical finding is to rely on ultrasound results when assessing fetal weight in the normal range. On the other hand, estimation of the weight of macrosomic fetuses based on abdominal examination before delivery is usually exaggerated, while the estimation of fetal size using ultrasound is reliable.

Conclusion

Estimating fetal weight with prenatal ultrasound is highly accurate. Clinical examination is more accurate in determining the weight of smaller fetuses and does not pay much attention to the estimation of higher weights and even leads to overestimation, while ultrasound is much more accurate in diagnosing fetal macrosomia (fetal weights more than 4000 g). It is recommended that the effect of clinical examination and ultrasound imaging on fetal weight estimation be further evaluated in a multicenter study by examining the relationship between factors influencing the accuracy of estimation.

Financial support and sponsorship

This study is based on a residency dissertation funded by our university.

Conflicts of interest

There are no conflicts of interest.