The present study was conducted at the Baghdad Teaching Hospital, Medical city, Baghdad, Iraq. Data were collected from January 1, 2023 to November 1, 2023. The present study used an analytical cross-sectional design. Informed consent was obtained from all participants prior to data collection. Verbal consent was obtained from all participants prior to data collection. An official letter of approval (no. 338) was obtained from the Scientific Committee of the Scientific Council of Obstetrics and Gynecology-Iraqi Board for Health Specializations, in accordance with the Declaration of Helsinki.

A total of 100 pregnant women with established preterm labour (gestational age, 28 to 36 weeks + 6 days) were included in the present study. Preterm labour was diagnosed based on documented uterine contractions and cervical dilation exceeding 4 cm. All deliveries occurred prior to 37 weeks of gestation. The gestational age was calculated depending on the last menstrual period (LMP) of the mother and the first trimester ultrasound scan. A full history and thorough general and obstetrical examinations were performed for all women.

Basic sociodemographic and obstetric data were collected [age, parity, gestational age, past medical history, body mass index (BMI) and birth weight]. A total of 10 cm³ of blood were collected from the pregnant women for general analyses: Complete blood count, renal function test, liver function test, thyroid function test, blood group and Rh factor. A vaginal and rectal swab sample were also obtained during a vaginal examination.

As the infection prevention and control settings in the hospital were not deemed as being of a high standard (in the hospital, due to the overcrowding of the wards, and the close proximity between patients made it difficult to maintain a safe distance between patients, increasing the risk of airborne and contact-based infections), the consultant gynaecologist decided to administer antibiotic therapy to all mothers with preterm labour (IV ceftriaxone vial 1 gm in a single dose, and in the case of allergy, vancomycin vial at 1 gm).

In the laboratory (private sector), using the VITEK-2 machine, the following procedures were performed: i) Inoculation and incubation: The specimen was inoculated with enrichment broth (nutrient) for 24 h and then transferred into the appropriate culture media (Blood agar, MacConkey agar or Sebouraud dextrose agar) (BioMérieux) to subculture, at the appropriate temperature and conditions for GBS growth (typically 35-37˚C for 24 h). ii) Isolation: The colony was examined for growth on the culture plates. GBS colonies typically appear as small, greyish-white colonies, with a surrounding zone of beta-haemolysis, on the blood agar. iii) Identification: A sterile loop was used to select a single colony and transfer it to the appropriate VITEK-2 identification card, designed for the Streptococcus species. The VITEK-2 system (BioMérieux) provided a profile of the organism based on its characteristics after (6-8 h), and generated a report that included the identification of the Streptococcus species, including GBS. The result was received after 3 days.

Following delivery, all neonates were followed-up for 1 week as follows: i) Those who required admission to the Neonatal Care Unit had blood cultures obtained, in the event that their admission lasted >3 days. ii) Those who were discharged from the Neonatal Care Unit of the hospital, had their follow-up performed by phone, for up to 1 week.

The inclusion criteria were women with singleton pregnancies, presenting with preterm labour (from 28 to 36 weeks + 6 days), with gestational age being diagnosed by LMP, confirmed by a report of the first trimester ultrasound. The exclusion criteria were as follows: Women pregnant with a foetus with congenital anomalies, women with premature rupture of membranes, and women with fever, an elevated white blood cell count, or other features suggestive of chorioamnionitis.

Statistical analysis was performed using the statistical package for social sciences (SPSS version 26; IBM Corp.). The Independent sample t-test was used to compare the continuous variables. Fisher's exact test was used for categorical variables. A two-tailed P-value ≤0.05 was considered to indicate a statistically significant difference.

The present study revealed that GBS was identified in 8% of women experiencing premature labour. Notably, GBS colonisation was more likely to be associated with early preterm (28-32 weeks), rather than late preterm (32-37 weeks) labour. A previous study conducted in Denmark by Feikin et al (9) found that among 84 women experiencing preterm labour, 14% were colonised at delivery with GBS. The study by Schwab et al (10) in Indonesia, included 23 women (term and preterm) and reported that 8/23 (35%) had GBS.

It is important to highlight the low prevalence of GBS that was detected in the present study. The previous meta-analysis by Ashary et al (8) identified three parameters that were associated with improving the detection of GBS: i) The site of sample collection: Studies that employed a rectovaginal sample reported higher detection rates than studies relying of vaginal samples alone. ii) Enrichment prior to culture: The meta-analysis reported that enrichment increased the detection rate of GBS by almost 2-fold compared to studies that did not use enrichment. iii) Detection method: The prevalence of GBS determined by the culture approach was calculated at 7.4%, but the immunological method indicated a frequency of 11.6%. Compared to the cultural and immunological approaches, the identification of GBS by molecular techniques yielded a high prevalence of 62% (8).

Although a rectovaginal sample was used in the present study, culture enrichment was not performed with the recommended sheep blood agar that increased detection. Therefore, it is reasonable to assume that the prevalence would significantly increase if culture enrichment and immunological or molecular approaches were employed in Iraq.

In the present study, obesity was significantly associated with GBS colonisation. This finding is in concordance with the study by Dahan-Saal et al (11), who reported that obesity was the most prevalent determinant of GBS colonisation, as it increased the risk of acquiring GBS by 19%. In the USA, the study by Stapelton et al (12) included 1,20,000 pregnant women and reported a 20% increase in the risk of miscarriage in moderately obese women (BMI, 30-40) and a 40% increase in cases of morbid obesity (BMI, ≥40). In another study, Kleweis et al (13) included 7,711 pregnant women and reported that obese gravidas were still 35% more likely than non-obese women to test positive for GBS. In the USA, Venkatesh et al (14) included 1,15,070 women with term deliveries and reported a significant rise in the frequency of GBS colonisation with a higher pre-pregnancy BMI.

The molecular mechanism behind heightened GBS colonisation in obese women remains unclear, while it may be associated with changes in the composition and functional characteristics of the gut microbiota.

In the present study, DM was also significantly linked to a higher rate of GBS infection. This finding is in concordance with the study by Field et al (15), who included 305 pregnant women and reported that women with an HbA1c level ≥6.5% were twice as likely to have GBS colonisation than women with an HbA1c level <6.5%. This association between DM and GBS colonisation may be attributed to the following reasons: i) DM alters immune cell function within the reproductive tract; and ii) glucose alters GBS growth and promotes biofilm production, which may promote colonisation (16).

A notable finding of the present study was that the proportion of vertical transmission of GBS was found to be 0%. This may be attributed to the study setting, as it was conducted in a tertiary centre, where intrapartum prophylactic antibiotics are administered early. In the USA, the CDC has reported that by using the strategy of maternal screening and the administration of intrapartum antibiotics, GBS infection among newborns has been reduced from 1.7-1.9 per 1,000 live births in the early 1990s, to 0.34-0.37 per 1,000 newborns in 2008(17). Yadeta (5) reported that all newborns exposed to IAP for ≥4 h were not colonised. However, newborns exposed to IAP for <4 h were colonised. The study by McNanley et al (18) demonstrated that the GBS vaginal colony counts decreased by 5-fold during 2 h of intravenous penicillin G administration and decreased by 50-fold within 4 h. Studies conducted in countries, such as Bangladesh and Eastern Ethiopia with limited access to IAP have reported vertical transmission rates as high as 38.0 and 45.02%, respectively (5,19).

Another reason for the low vertical transmission may be attributed to the small sample size of the present study. Other than IAP, Gizachew et al (20) reported that commitment to antenatal care follow-up was the most critical factor preventing vertical transmission, as pregnant mothers who attended four to five antenatal care visits throughout their pregnancy were 20.9% less likely to vertically transfer colonised GBS to their babies.

The demonstrated association of maternal GBS colonisation with preterm labour, highlights the importance of vaccination. In 2020, Procter et al (21) conducted a global analysis of 140 million pregnant women across 183 countries, and concluded that a GBS vaccination was successful in avoiding up to 4,07,000 preterm births.

In conclusion, although the present study found that vertical transmission can be controlled by the proper administration of IAP, babies of mothers with maternal colonisation had poor outcomes 5/8, (62.5% died), as GBS colonisation was significantly associated with A lower gestational age (which was significantly associated with neonatal mortality). Moreover, the present study effectively consolidated the association between maternal GBS and both DM and obesity. Therefore, women with DM and obesity require special attention for early detection, and therefore, the early management of their condition.