A demographically specific fundal height (FH) growth curve derived from local pregnant women with specific ethnicity, socioeconomics, or nutritional status [
However, previous findings showed that in women of the same geographical areas, there were still other independent determinants of FH. These determinants included maternal height, maternal weight, body mass index (BMI), parity, fetal sex, and gestational age (GA) [
Application of FH growth curve derived from “general” population to monitor or screen abnormal intrauterine growth in obese or slim women may result in over- or underinvestigation and/or intervention. Applying separate FH growth curves specific for women body shapes may be more beneficial [
In Thailand, separate FH growth curves according to prepregnant BMI, <20, 20–24, and >24 kg/m2, and GA assessed from ultrasound [
The present study aimed to develop fundal height growth curves for underweight (BMI < 18.5 kg/m2) and overweight and obese (BMI ≥ 25.0 kg/m2) pregnant women in the northern part of Thailand, based on GA from LMP and/or ultrasound following routine practice.
Antenatal care (ANC) and delivery records of women between January 2009 and March 2011 were retrospectively collected from two secondary care and two tertiary care hospitals in the northern part of Thailand.
The study included women whose GA was less than 20 weeks when attending the first ANC visit. The following pregnant women were excluded: non-Thai, minority groups, unreliable GA, those with comorbidity, current smokers, those who used alcohol or addictive substance during pregnancy, those who developed medical complication during pregnancy: diabetes, hypertension, and anemia, those who had twins, uterine tumor, polyhydramnios, oligohydramnios, intrauterine growth restriction, abnormal fetal presentation, preterm or postterm, low birth weight (<2,500 g) or relatively large baby (≥4,000 g), or congenital anomaly.
Prepregnancy BMI was calculated from prepregnancy body weight (in kg) divided by square of height (in meter).
Pregnant women were categorized into 3 groups based on WHO criteria [ Underweight: BMI < 18.5 kg/m2. Normal weight: BMI 18.5–24.9 kg/m2. Overweight and obese: BMI ≥ 25.0 kg/m2.
Gestational age was assessed from 2 sources: (1) based on first day of LMP in women with regular menstruation history, who could recall the exact date and those whose FH was correlated with GA, or GA by LMP was no more than 1 week different from ultrasound, (2) from ultrasound performed in the first half of pregnancy, in women who did not fulfill criteria (1).
The measurement of FH followed routine practice of the four settings, which was adopted from ANC practice recommended by The Division of Maternal and Child Health and The Ministry of Health. All measurements were conducted by nurses or physicians in ANC clinics who had at least 2 years of experiences. This was based on the finding that such experiences reduced measurement errors and bias [
Key information included GA, FH, height, and prepregnancy weight. All information was extracted from ANC records, delivery records, and other related medical records.
Data analysis was done considering the differences of GA calculated by different methods and the differences in FH measurements by different settings and by standardization methods.
The general characteristics of pregnant women were presented by frequency, percentages, mean, and standard deviation. Nonparametric tests for trend were applied to test the differences among the 3 BMI groups.
The mean FH (cm) for each gestational week between underweight and normal weight and between overweight and obese and normal weight pregnant women was compared by
Polynomial equations of the 10th, 50th, and 90th percentiles of FH on GA among the underweight, normal weight, and overweight and obese pregnant women were conducted by multilevel models for continuous data. Smoothed curves were drawn from final quadratic regression models.
The study protocol was approved by the Research Ethics Committee, Faculty of Medicine, Chiang Mai University, and the research ethics committee of the four hospitals.
Study subjects were comprised of 1,038 pregnant women, categorized by BMI into underweight (
Characteristics of pregnant women.
Characteristics | Prepregnancy BMI (kg/m2) |
Global
|
|||||
---|---|---|---|---|---|---|---|
Underweight (<18.5) | Normal weight (18.5–24.9) | Overweight and obese (≥25.0) | |||||
( |
( |
( |
|||||
Mean | ±SD | Mean | ±SD | Mean | ±SD | ||
Maternal age (year) | 22.8 | ±5.0 | 25.9 | ±6.3 | 28.1 | ±5.7 | <0.001 |
Maternal height (cm) | 157.5 | ±6.1 | 155.6 | ±5.4 | 156.1 | ±5.6 | 0.011 |
Prepregnancy weight (kg) | 42.9 | ±4.0 | 51.5 | ±5.4 | 69.0 | ±8.0 | <0.001 |
Prepregnancy BMI (kg/m2) | 17.3 | ±1.1 | 21.2 | ±1.8 | 28.3 | ±2.7 | <0.001 |
Total weight gain (kg) | 13.9 | ±4.0 | 13.9 | ±4.5 | 11.2 | ±5.2 | <0.001 |
Gestational weight gain** ( |
<0.001 | ||||||
Less than recommended | 79 | 38.0 | 197 | 29.9 | 27 | 16.0 | |
Within recommended | 99 | 47.6 | 273 | 41.4 | 56 | 33.1 | |
More than recommended | 30 | 14.4 | 189 | 28.7 | 86 | 50.9 | |
Parity ( |
<0.001 | ||||||
Nulliparous | 143 | 68.7 | 333 | 50.4 | 47 | 27.8 | |
Multiparous | 65 | 31.3 | 328 | 49.6 | 122 | 72.2 | |
GA at delivery (wk) | 39.1 | ±1.1 | 39.2 | ±1.1 | 39.3 | ±1.1 | 0.107 |
Infant’s sex ( |
0.918 | ||||||
Female | 101 | 48.6 | 294 | 44.5 | 84 | 49.7 | |
Male | 107 | 51.4 | 367 | 55.5 | 85 | 50.3 | |
Birth weight (gm) | 3,035.0 | ±318.4 | 3,126.5 | ±327.0 | 3,201.0 | ±302.3 | <0.001 |
| |||||||
Settings ( |
0.754 | ||||||
Secondary care hospitals | 140 | 67.3 | 445 | 67.3 | 111 | 65.7 | |
Tertiary care hospitals | 68 | 32.7 | 216 | 32.7 | 58 | 34.3 | |
Gestational age by ( |
0.051 | ||||||
LMP | 115 | 55.3 | 424 | 64.2 | 109 | 64.5 | |
Ultrasound | 93 | 44.7 | 237 | 35.8 | 60 | 35.5 | |
GA at first ANC (wk) | 14.2 | ±5.2 | 12.7 | ±4.8 | 12.6 | ±4.9 | 0.001 |
GA at ultrasound (wk) | 16.9 | ±5.4 | 15.8 | ±5.1 | 15.2 | ±5.3 | 0.037 |
Frequency of ANC (per woman) | 6.9 | ±2.2 | 7.3 | ±2.1 | 7.5 | ±2.2 | 0.020 |
BMI: body mass index; GA: gestational age; LMP: last menstrual period; ANC: antenatal care.
In this group, FH increased from 19.1 cm (±1.7) at 20-week GA to 34.5 cm (±2.3) at 40-week GA. The average increasing rate was 0.8 cm/wk. The highest rate was observed at 1.0 cm/wk between 20 and 32 weeks, declining to 0.6 cm/wk between 33 and 36 weeks, and to 0.2 cm/wk between 37 and 40 weeks (Table
Mean and standard deviation of fundal height (in centimeters) for each gestational age in underweight, normal weight, and overweight and obese pregnant women.
GA (wk) | Fundal height (cm) | |||||||
---|---|---|---|---|---|---|---|---|
Underweight |
Normal weight |
|
|
| ||||
Number | Mean ± SD | Number | Mean ± SD | Number | Mean ± SD | |||
20 | 35 |
|
104 |
|
0.933 | 27 |
|
0.867 |
21 | 31 |
|
90 |
|
0.780 | 23 |
|
0.628 |
22 | 23 |
|
72 |
|
0.874 | 24 |
|
0.276 |
23 | 25 |
|
83 |
|
0.444 | 15 |
|
0.901 |
24 | 53 |
|
167 |
|
0.020 | 46 |
|
0.959 |
25 | 51 |
|
145 |
|
0.808 | 39 |
|
0.896 |
26 | 22 |
|
73 |
|
0.350 | 31 |
|
0.054 |
27 | 32 |
|
90 |
|
0.259 | 20 |
|
0.957 |
28 | 62 |
|
225 |
|
0.034 | 62 |
|
0.077 |
29 | 54 |
|
167 |
|
0.138 | 47 |
|
0.692 |
30 | 66 |
|
223 |
|
0.018 | 63 |
|
0.001 |
31 | 73 |
|
209 |
|
0.240 | 54 |
|
0.050 |
32 | 87 |
|
278 |
|
0.045 | 73 |
|
<0.001 |
33 | 70 |
|
249 |
|
0.231 | 67 |
|
<0.001 |
34 | 89 |
|
249 |
|
<0.001 | 71 |
|
0.048 |
35 | 73 |
|
251 |
|
0.082 | 67 |
|
<0.001 |
36 | 94 |
|
297 |
|
<0.001 | 82 |
|
0.061 |
37 | 145 |
|
481 |
|
<0.001 | 113 |
|
<0.001 |
38 | 164 |
|
529 |
|
0.003 | 147 |
|
<0.001 |
39 | 151 |
|
495 |
|
<0.001 | 116 |
|
<0.001 |
40 | 86 |
|
279 |
|
0.002 | 94 |
|
0.002 |
GA: gestational age.
The FH in this group increased from 19.1 cm (±1.9) at 20-week GA to 35.4 cm (±2.3) at 40-week GA. The average rate was 0.8 cm/wk, highest between 20 and 32 week at 1.0 cm/wk, declining to 0.8 cm/wk between 33 and 36 weeks, and to 0.2 cm/wk between 37 and 40 weeks (Table
In this last group, FH increased from 19.2 cm (±2.0) at 20-week GA to 36.2 cm (±2.2) at 40-week GA. The average rate was 0.9 cm/wk, highest between 20 and 32 week at 1.1 cm/wk, declining to 0.7 cm/wk between 33 and 36 weeks, and to 0.2 cm/wk between 37 and 40 weeks (Table
At 20 weeks, the FH of the two groups was similar. However, between 33 and 36 weeks, the increasing rate in the underweight was 0.2 cm/wk lower than in the normal weight group, resulting in a difference of 0.9 cm at week 40. Week by week comparisons showed significant differences between weeks 34 and 40 (Table
At 20 weeks, the two groups were also similar in FH. The increasing rate in overweight and obese was 0.1 cm/wk higher until week 32, resulting in a 0.8 cm difference at week 40. Through comparisons by weeks, the FH was significantly different between weeks 30 and 40 (Table
The FH obtained from quadratic equations allowing for random (individual) effect was estimated by the following equations.
Underweight:
Normal weight:
Overweight and obese:
The above equations explained 84%, 86%, and 87% of the variation (
The final FH growth curve of underweight, normal weight, and overweight and obese pregnant women (Figure
Coefficients at the 10th, 50th, and 90th percentiles for fundal height prediction equations in underweight, normal weight, and overweight and obese pregnant women from multilevel models.
Parameters | Coefficient (cm) | ||
---|---|---|---|
10th percentiles | 50th percentiles | 90th percentiles | |
Underweight | |||
Constant |
|
|
|
GA (wk) | 2.550561 | 2.345531 | 2.314052 |
GA2 (wk) |
|
|
|
Normal weight | |||
Constant |
|
|
|
GA (wk) | 2.943811 | 2.392514 | 1.914523 |
GA2 (wk) |
|
|
|
Overweight and obese | |||
Constant |
|
|
|
GA (wk) | 2.769345 | 2.639944 | 2.115199 |
GA2 (wk) |
|
|
|
GA: gestational age.
Fundal height growth curve at the 90th, 50th, and 10th percentiles derived from 169 overweight and obese pregnant women (1,281 visits) (dash lines), 661 normal weight pregnant women (4,756 visits) (solid lines), and 208 underweight pregnant women (1,486 visits) (dot lines).
Overall comparisons of the FH growth curves among the underweight, the normal weight, and the overweight and obese pregnant women showed that the 50th percentiles of the three groups departed at weeks 22-23. The departures were more obvious at weeks 30–32. The underweight line was 0.1–0.4 cm below the normal line at weeks 23–31 and 0.5–0.8 cm at weeks 32–40. In the opposite direction, the overweight and obese line was 0.1–0.4 cm above the normal line at weeks 22–29 and 0.6–0.8 cm at weeks 30–40 (Figure
The 90th percentile line of the underweight was below the normal weight throughout pregnancy, approximately by 0.4–1.2 cm. The 10th percentile line of the overweight and obese was above the normal weight throughout pregnancy, with the average of 0.4–1.4 cm (Figure
The FH growth curves for the underweight, normal weight, and overweight and obese pregnant women were different regarding the 10th, 50th, and 90th percentiles and the inclining rates per week (Figure
Abdominal subcutaneous fat thickness or subcutaneous adipose tissue thickness is directly correlated with FH as FH was measured with nonelastic tapes. Women with abdominal subcutaneous fat thickness were likely to have higher FH than those with thinner abdominal subcutaneous fat. Subcutaneous adipose tissue thickness of anterior abdomen in nonpregnant women with BMI <25, 25–29.9, 30–39.9, and ≥40 kg/m2 increased from 10.6 to 17.6, 22.4, and 26.8 mm [
Fetal weight and birth weight (BW) were directly correlated with FH [
Prepregnancy BMI influenced fetal weight and BW [
Gestational weight gain was correlated with BW [
Parity or birth order was positively correlated with BW [
The effect of maternal age on BW varied between studies. Some studies claimed no correlation [
The above dissimilarities indicated the necessity to develop FH growth curves specifically for women with different body structures. Women with “average” body structure may use a FH growth curve that developed for normal population, while women with slim or obese body shapes should have their own FH growth curves for monitoring and screening abnormal intrauterine growth.
Application of FH growth curves specific for women body shape may reduce an over- or underinvestigation and/or -intervention. For example, in the underweight pregnant women, if a general FH growth curve was applied, FH below the 10th percentiles (size < date) would be detected in 15.4%, and FH above the 90th percentiles (size > date) in 1.2% (Figure
Fundal height (FH) of underweight and overweight and obese pregnant women as screened by different growth curves; (a) underweight pregnant women versus normal population curve; (b) underweight pregnant women versus underweight curve; (c) overweight and obese pregnant women versus normal curve; (d) overweight and obese pregnant women versus overweight and obese curve.
In the overweight and obese pregnant women, if a general FH growth curve was applied, FH above the 90th percentiles (size > date) would be detected in 11.1% and that below the 10th percentiles (size < date) in 3.0% (Figure
Body mass index categorization in the present study followed the WHO criteria [
However, the developed FH growth curves for the underweight and overweight and obese pregnant women in this study was based on routine ANC practice of the four university affiliated hospitals in the upper northern part of Thailand. Generalization to other settings with different context, including the methods of FH measurement and the methods of GA assessments, may be limited.
Furthermore, the measurement of FH in normal practice is still considered “subjective” to intraobserver and interobserver errors. A standardized method should be reinforced, such as frequent validation or calibration, as we believe that simple FH measurement is of great value as a screening tool for routine antenatal care practice, especially in areas where health resources are limited.
Fundal height growth curves of the underweight (BMI < 18.5 kg/m2) and overweight and obese (BMI ≥ 25.0 kg/m2) women were different from the normal weight. In monitoring or screening for abnormal intrauterine growth in slim or obese women, FH growth curves specifically developed for such women should be applied. This may reduce an over- or underinvestigation and/or -intervention as a consequence of an inappropriate application of FH growth curve for normal weight women.
The authors declare that they have no conflict of interests.
The authors wish to thank the authorities of Phayao, Lamphun, Nakornping, and Lampang Hospitals for their support and the Faculty of Medicine, Chiang Mai University, for the study grant.