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ORIGINAL ARTICLE
Year : 2014  |  Volume : 27  |  Issue : 3  |  Page : 518-523

The effect of body mass index on cervical characteristics and on the length of gestation in low-risk pregnancies


1 Department of Obstetrics and Gynecology, Faculty of Medicine, Menoufia University, Menoufia, Egypt
2 Department of Obstetrics and Gynecology, Faculty of Medicine, Ain Shams University, Cairo, Egypt

Date of Submission05-Jan-2014
Date of Acceptance30-Mar-2014
Date of Web Publication26-Nov-2014

Correspondence Address:
Sheren Gamil Abo Elyazid Elmenawy
Department of Obstetrics and Gynecology, Helwan General Hospital, 15 May City, Unite 21, Group 5, Block 9, No. 10, Cairo
Egypt
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/1110-2098.145499

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  Abstract 

Objective
This study was undertaken to evaluate the effect of different BMIs on the cervical diameter and its relation to the length of gestation among low-risk pregnant Egyptian women.
Background
The effect of BMI on the length of gestation is not clearly documented. There are claims that obese women may have longer gestations and longer cervices compared with normal and underweight women through changes in cervical diameters, which have an effect on the pregnancy outcome.
Participants and methods
This observational cohort study included 100 pregnant women from a total of 120 women at Helwan General Hospital (Egypt). All enrolled women were primigravidae with singleton pregnancies at 20-22 weeks' gestation. Enrolled women were equally allocated into four groups according to their BMIs.
A vaginal ultrasonography was performed to measure the cervical length and width. Enrolled participants were followed up until delivery after recording their mean cervical length and width by transvaginal ultrasonography.
Results
There were five preterm births and five post-term births, representing 5 and 5% of the total cohort study. One neonatal death occurred due to prematurity, and four women developed postpartum hemorrhage with no maternal mortality. The incidence of SPTB was high among underweight women (12%) from a total of 25 women, whereas the incidence of post-term delivery was common among overweight and obese women, representing 8 versus 12%, respectively.
Conclusion
Underweight women are more liable to have more preterm delivery and low birth weight. However, overweight and obese women are less vulnerable to preterm delivery. They have a tendency for post-term gestation, increased incidence of cesarean section and macrosomia.

Keywords: BMI, cervical length and width


How to cite this article:
Kandeel MS, Sanad ZF, Sayyed TM, Elyazid Elmenawy SA. The effect of body mass index on cervical characteristics and on the length of gestation in low-risk pregnancies. Menoufia Med J 2014;27:518-23

How to cite this URL:
Kandeel MS, Sanad ZF, Sayyed TM, Elyazid Elmenawy SA. The effect of body mass index on cervical characteristics and on the length of gestation in low-risk pregnancies. Menoufia Med J [serial online] 2014 [cited 2020 Feb 27];27:518-23. Available from: http://www.mmj.eg.net/text.asp?2014/27/3/518/145499


  Introduction Top


The effect of BMI on the length of gestation is not clearly documented. There are claims that obese women may have longer gestations compared with normal or underweight women [1] . Whether BMI exerts such an effect through changes in the cervical length and width is unknown.

A short cervical length below 15 mm at 22-24 weeks' gestation is associated with increased risk of preterm delivery [2],[3] as the main cause of neonatal death [1] . Infact, there was a 3% increase in the odds of a spontaneous preterm birth for every 1 mm of cervical shortening between ultrasonographic scans among women with a short cervix [4] . Furthermore, spontaneous preterm birth less than 36weeks' gestation is associated with a short cervix below 25 mm [5] . Routine assessment of the cervical length at 18-22 weeks' of gestation provides a sensitive prediction of spontaneous preterm delivery [2],[3] and can be carried out simultaneously with the fetal anomaly scan at a gestational age just before fetal viability. The likelihood of a spontaneous preterm delivery increases as the cervical length decreases [3]. To the best of our knowledge, no studies have been conducted to determine the relationship between the cervical length and width and post-term labor. Whether women with different BMIs have different mean cervical lengths and widths affecting the duration of gestations remains unknown.


  Participants and methods Top


Study population

This observational cohort study was carried out in the Helwan General Hospital (Egypt) from July 2012 to April 2013, and included 100 pregnant women from a total of 120 primigravidae with singleton pregnancies (20 women dropped out). Three women dropped out of the underweight women [group I (n = 25)] and were replaced by another three with the same BMI; 10 women were lost to follow-up in the normal-weight women [group II (n = 25)] and were replaced by another 10 women with the same BMI. Also, five women dropped out of the overweight group [group III (n = 25)] and were replaced by another five women with the same BMI; two more obese women dropped out of group IV (n = 25) and were replaced by another two women with the same BMI.

Patients were selected from those attending the outpatient clinic of the hospital at 20-22 weeks' gestation. Maternal height and weight were measured, and the BMI was calculated (kg/m 2 ). Enrolled women were allocated equally into four groups according to the maternal obesity classification as defined by the National Institute of Health [5] as follows: group I consisted of underweight women with a BMI of 18.5 kg/m 2 or less; group II consisted of women with normal weight with a BMI between 18.5 and 24.9 kg/m 2 ; group III consisted of overweight women with a BMI ranging between 25 and 29.9 kg/m 2 ; and group IV consisted of obese women with a BMI equal to or more than 30 kg/m 2 . Estimation of the gestational age was based on the first day of the last menstrual period for pregnant women who were sure of their dates. Women with any of the following criteria were excluded from the study:

  1. First-trimester bleeding, low-lying placenta or evidence of uteroplacental insufficiency;
  2. A first-trimester scan that was incompatible with their menstrual gestational age according to their reported last menstrual period;
  3. Myomatous or malformed uterus;
  4. Multiple pregnancy and hydramnios;
  5. premature rupture of membranes;
  6. Cervical incompetence;
  7. Medical disorders such as diabetes mellitus and pregnancy-induced hypertension;
  8. Recurrent urinary tract infection during the current pregnancy.


Patients who met the inclusion criteria were invited to participate in this study. The study was discussed with the patient and a written consent was taken from women who agreed to participate in the study, which was approved by the hospital ethics committee.

Thorough history taking and physical examination were performed for all recruited women. A vaginal ultrasonography was performed at enrollment to measure the cervical length and width in the enrolled participants using a multifrequency 5-7-mHz transducer (Toshiba Eccocee; Toshiba, Japan). Patients with empty bladders were placed in the dorsal lithotomy position. A sagittal view of the cervix was obtained by placing the probe in the anterior fornix of the vagina, avoiding undue pressure on the cervix and demonstrating the endocervical mucosa along the length of the canal. Calipers were used to measure the distance between the internal orifice and the external cervical orifice. The cervix was observed for about 3 min to check for any changes, particularly contractions (observed in <1% patients). The shortest measurement obtained was recorded. The cervical width was measured in the same plane as the cervical length; it is the distance from anterior and posterior cervix midway between the internal and the external cervical orifice ([Figure 1]).
Figure 1: The transvaginal ultrasonography image of a normal cervix (cervical length = 33 mm and cervical width = 19 mm).

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Patient's characteristics, including demographic data and previous obstetric and medical history, were obtained at their first antenatal visit to the hospital. These data were recorded into a hand-held antenatal card. Ultrasonographic findings and patient demographic details were stored in a computerized database.

Statistical analyses

All statistical calculations were performed using the computer program statistical package for the social science (SPSS; SPSS Inc., Chicago, Illinois, USA). Data were collected and tabulated according to standard statistical methods.


  Results Top


Regarding the BMI, the mean cervical length was the shortest (27.4 mm) among women with BMI less than 18.5 kg/m 2 with a highly statistically significant difference between them and other BMI subgroups (II, III, IV) (P < 0.001; [Table 1]).
Table 1: Cervical length in different groups according to the BMI at 20-22 weeks'gestation


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There was a significant statistical difference between the mean cervical width in group II and other groups ([Table 2]).
Table 2: Cervical width in different groups according to the BMI at 20-22 eeks' gestation


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Preterm delivery constituted 5% of the total study group, with the shortest recorded mean cervical length at 20-22 weeks (28.20 mm), which had a significant statistical difference (P = 0.035). Post-term delivery constituted 5% of the study group with the longest mean cervical length (41.00 mm) ([Table 3]).
Table 3: Cervical length at 20-22 weeks' of gestation and the length of gestation


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Group I consisted of underweight women who had three (12%) preterm deliveries with an increased relative risk (RR) of preterm delivery (RR = 1.5). Group II consisted of normal-weight women who had two (8%) preterm deliveries. Groups III and IV consisted of overweight and obese women who developed two and three post-term deliveries, respectively, representing 10% of the total of both groups ([Table 4]).
Table 4: Length of gestation at labor in different groups according to their BMI at 20-22 weeks' gestation


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There was a statistically highly significant positive correlation between BMI, the cervical length (P < 0.001, R = 0.861; [Figure 2]), and the gestational length (P < 0.001, R = 0.565; [Figure 3]).
Figure 2: The BMI had a positive correlation with the cervical length at 20-22 weeks' gestation (R = 0.861), which was highly statistically significant (P < 0.001). TVUS, transvaginal ultrasonography.

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Figure 3: There was a positive correlation between the BMI and the length of gestation at 20-22 weeks' gestation (R = 0.565), which was highly statistically significant (P < 0.001).

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[Figure 4] shows that the cervical length was distributed approximately normally, with some skewness at the lower end. The mean cervical length value was 33.7 mm.
Figure 4: The cervical length frequency distribution (histogram) shows that the cervical length was approximately distributed normally with some skewness at the lower end. The median (and the mean cervical length) value was 33.7 mm. TVUS, transvaginal ultrasonography.

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[Table 5] depicts the mode of delivery in the four different groups, whereas in [Table 6], neonatal outcomes were tabulated and revealed that the underweight group had 36% incidence of low birth weight (LBW) with a highly statistically significant difference between them and group IV obese women (P < 0.001). Groups III and IV showed an incidence of macrosomia of 8 versus 4%, respectively.
Table 5: Neonatal outcome (birth weight) in different groups according to the BMI


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Table 6: Mode of delivery in different groups according to the BMI


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  Discussion Top


The impact of low or increased BMI in the general population on the cervical length has been the focus of many studies, but there are few studies pertaining to pregnancy and they are from the western countries [6]. In the USA, the incidence of obesity among pregnant women ranges from 18.5 to 38.3% [7] .

This cohort study has shown that both overweight and obese women had a longer mean cervical length than women of normal weight when measured at 20-22 weeks' gestation, and underweight women had the shortest mean cervical length with a highly significant statistical difference among all groups. This finding is in agreement with that of Hendler et al. [8] , who studied 2929 women and found an increased cervical length in overweight and obese women compared with nonobese women (36.5 ± 8.4 vs. 34.9 ± 8.1 mm; P < 0.0001). Similar results were found in Thai women in a study conducted by Liabsuetrakul et al. [9] .

The incidence of preterm delivery in the current study was higher in group I women with BMI less than 18.5 kg/m 2 (12%) compared with women in groups II, III, and IV (8, 0, and 0%, respectively) with an increased RR (1.5). Ehrenberg et al. [10] reported 16.3% as the incidence of SPTB in women with BMI less than 19.8 kg/m 2 in their cohort study on 15 196 women. Decreased intake of calories, proteins, vitamins, and minerals, which are often associated with decreased BMI, may explain the higher rate of SPTB in thin patients [11] .

In contrast, a retrospective cohort study by Bhattacharya et al. [12] , which involved 24 241women, had shown 8.5, 6.8, 6.1, and 14.2% incidence of SPTB for similar BMI subgroups, respectively. This higher incidence of SPTB in the overweight and the obese groups (groups III and IV) is contradictory to the current study results. It might be due to the presence of other risk factors in their study series for preterm labor during pregnancy such as gestational hypertension, preeclampsia, gestational diabetes, polyhydramnios, bacterial vaginosis, and preterm premature rupture of membrane in their study participants. Our study inclusion criteria did not involve such risk factors.

The incidence of post-term delivery was 10% in the total number of patients in groups III and IV in our study, whereas Kiran et al. [13] reported a 41% incidence of postdates in their obese group through an observational study that included 8350 women.

The present study demonstrated that the mean cervical length measured at 20-24 weeks in low-risk populations was 33.3 mm less than that reported in other studies. Other studies reported a longer mean cervical length (38 mm by Heath et al. [3] and 37 mm by Palma-Dias et al. [1]. This difference might be due to the larger sample size in their studies and racial differences.

The mean cervical length in women who had preterm delivery (≤28.2 mm) was shorter than that in nonpreterm delivery groups (36.6 and 41 mm in term and post-term deliveries, respectively). Similar findings were reported by Andersen et al. [14] and Iams et al. [2] who recorded mean cervical lengths of 39 mm or less and 30 mm or less in preterm births below 37 and 35 weeks' gestation, respectively. This difference in the mean cervical length may be due to racial differences, differences in their obstetric history, and different sample sizes.

We found that women aged less than 20 years had the shortest mean cervical length (30.5 mm) at cervical scanning. Palma-Dias et al. [1] and Erasmus et al. [15] reported longer mean cervical lengths in women aged less than 20 years in their series (34.4 and 31.7 mm, respectively).

The incidence of caesarean section was more common among overweight and obese women, which was 16 and 36%, respectively, compared with 4 and 8% in groups I and II, respectively, but the difference was not statistically significant. This is in agreement with the results of a retrospective cohort study by Bhattacharya et al. [12] , who showed a higher incidence among obese women (73.5%). The presence of other risk factors of cesarean section in previous investigators' studies may account for their higher incidence of caesarean sections.

The incidence of LBW was the highest in group I at 36%. Similar results were found in a prospective study conducted by Sahu et al. [6] , who reported the highest incidence of LBW in their low BMI group, which consisted of 380 (23.9%) women. In contrast, the incidence of LBW was reported to be higher (19.8%) among obese women by Bhattacharya et al. [12] . This high incidence may be due to obesity-associated risk factors such as preeclampsia, gestational diabetes, preterm premature rupture of membrane and bacterial vaginosis, which was not confirmed with our results.

Macrosomia as an obstetric outcome was seen only among overweight and obese groups and constituted 8 and 4%, respectively, whereas the incidence of macrosomia was 10.6 and 29.6% in overweight and obese groups, respectively, as reported by Bhattacharya et al. [12] . Obesity increases maternal insulin resistance. In addition, there is an increased fetoplacental availability of glucose, free fatty acids, and amino acids, leading to the higher incidence of macrosomia.

The small sample size was an important limitation of the current study as a larger sample might have yielded more significant statistical results. In addition, more data would have been gained about cervical evaluation during pregnancy in different groups if another setting of cervical scanning was established in this study.


  Conclusion Top


Overweight and obese women are less vulnerable to preterm delivery. However, they have a tendency for post-term gestation, increased incidence of cesarean section and macrosomia. Underweight women are more liable to have preterm delivery and LBW. The presence of a short cervix in women with low BMI is not necessarily a prognostic factor for preterm delivery unless it was associated with other risk factors.


  Acknowledgements Top


Conflicts of interest

There are no conflicts of interest.



 
  References Top

1.Palma-Dias RS, Fonseca MM, Stein NR, Schmidt AP, Magalhaes JM. Relation of cervical length at 22-24 weeks of gestation to demographic characteristics and obstetric history. Braz J Med Bio Res 2004; 37 :737-744.  Back to cited text no. 1
    
2. Iams JD, Goldenberg RL, Meis PJ, et al. The length of the cervix and the risk of spontaneous delivery. N Engl J Med 1996; 334 :567-572.  Back to cited text no. 2
    
3. Heath VCF, Southall TR, Souka AP, Elisseou A, Nicolaides KH. Cervical length at 23 weeks of gestation: prediction of spontaneous preterm delivery. Ultrasound Obstet Gynecol 1998; 12 :312-317.  Back to cited text no. 3
    
4. Uyar Y, Erbay G, Demir BC, Baytur Y. Comparison of the Bishop score, body mass index and trans vaginal cervical length in predicting the success of labor induction. Arch Gynecol Obstet 2009; 280 :357-362.  Back to cited text no. 4
    
5. National Institute for Health and Clinical Excellence (NICE). Induction of labor: clinical guideline; 2008. Available at: http://www.rcog.org.uk   Back to cited text no. 5
    
6. Sahu MT, Agarwal A, Das V, Pandey A. Impact of maternal body mass index on obstetric outcome. J Obstet Gynaecol Res 2007; 33 :655-659.  Back to cited text no. 6
    
7. Galtier-Dereure F, Boegner C, Bringer I. Obesity and pregnancy; complication and cost. Am J Clin Nutr 2000; 71 :12425-12485.  Back to cited text no. 7
    
8. Hendler I, Goldenberg RL, Mercer BM, et al. The Preterm Prediction Study: association between maternal body mass index and spontaneous and indicated preterm birth. Am J Obstet Gynecol 2005; 192 :882-886.  Back to cited text no. 8
    
9. Liabsuetrakul T, Suntharasaj T, Suwanrath C, Leetanaporn R, Rattanaprueksachart R, Tuntiseranee P. Serial translabial sonographic measurement of cervical dimensions between 24 and 34 weeks' gestation in pregnant Thai women. Ultrasound Obstet Gynecol 2002; 20 :168-173.  Back to cited text no. 9
    
10.Ehrenberg HM, Dierker L, Milluzzi C, Mercer BM. Low maternal weight, failure to thrive in pregnancy, and adverse pregnancy outcomes. Am J Obstet Gynecol 2003; 189 :1726-1730.  Back to cited text no. 10
    
11.Neggers Y, Goldenberg RL, Robert L. Some thoughts on body mass index, micronutrient, intake and pregnancy outcome. J Nutr 2003; 133 :1737-1740.  Back to cited text no. 11
    
12.Bhattacharya S, Campbell DM, Liston WA. Effect of body mass index on pregnancy outcomes in nulliparous women delivering singleton babies. BMC Pub Health 2007; 7 :168-175.  Back to cited text no. 12
    
13.Kiran UTS, Hemmadi S, Bethel J, Evans J. Outcome of pregnancy in a woman with an increased body mass index. Br J Obstet Gynecol 2005; 112 :768-772.  Back to cited text no. 13
    
14.Andersen HF, Nugent CE, Wanty SD, Hayashi RH. Prediction of risk for preterm delivery by ultrasonographic measurement of cervical length. Am J Obstet Gynecol 1990; 163 :859-867.  Back to cited text no. 14
    
15.Erasmus I, Nicolaou E, van Gelderen CJ, Nicolaides KH. Cervical length at 23 weeks' gestation - relation to demographic characteristics and previous obstetric history in South African women. S Afr Med J 2005; 95 :691-695.  Back to cited text no. 15
    


    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4]
 
 
    Tables

  [Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6]


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