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Research Article | Volume 11 Issue 8 (August, 2025) | Pages 562 - 571
A Case Control Study to Evaluate Risk Factors of Ectopic Pregnancy
 ,
 ,
1
Senior Resident, Senior resident, Dept of Obstetrics and Gynaecology, Kakdwip superspeciality Hospital, West Bengal India
2
Senior Resident, Chest Medicine, Jangipur Superspeciality Hospital, west Bengal India
3
Ex professor and HOD, Dept of Gynaecology and Obstetrics, Gouri Devi institute of medical science, Durgapur, west Bengal, India
Under a Creative Commons license
Open Access
Received
July 3, 2025
Revised
July 18, 2025
Accepted
Aug. 5, 2025
Published
Aug. 19, 2025
Abstract

Background: Ectopic pregnancy (EP) remains a significant cause of maternal morbidity and mortality worldwide. Identifying risk factors in different populations can improve early diagnosis and prevention strategies. Objective: To assess risk factors associated with ectopic pregnancy and compare them with those of intrauterine pregnancies. Methods: A hospital-based prospective case–control study was conducted at Nilratan Sircar Medical College, Kolkata, between January 2021 and July 2022. Sixty-five women with confirmed EP were recruited as cases, and 65 women with intrauterine pregnancies (first trimester) served as controls. Data on sociodemographic variables, obstetric and gynaecological history, and contraceptive practices were collected and analysed using chi-square and t-tests. Odds ratios (ORs) with 95% confidence intervals (CIs) were calculated, with significance set at p < 0.05.Results: Previous ectopic pregnancy (15.4% vs. 1.5%, OR 11.6, 95% CI: 1.4–93.8, p = 0.005), pelvic inflammatory disease (27.7% vs. 12.3%, OR 2.7, 95% CI: 1.1–6.8, p = 0.028), tubal sterilisation (6.2% vs. 0%, OR 9.6, 95% CI: 0.5–181.8, p = 0.042), and intrauterine device use (21.5% vs. 3.1%, OR 8.7, 95% CI: 1.9–39.8, p = 0.001) were significantly more frequent among cases. No significant associations were observed for infertility, genital tuberculosis, or dilatation and curettage. The most common presenting symptoms among cases were abdominal pain (83.1%) and amenorrhoea (46.4%). Mean haemoglobin was significantly lower in cases (7.08 g/dL) compared with controls (8.75 g/dL, p = 0.009).Conclusion: Previous ectopic pregnancy, pelvic inflammatory disease, tubal sterilisation, and IUD use significantly increased the odds of ectopic pregnancy. Strengthening reproductive health counselling and early screening in high-risk women may reduce morbidity and improve maternal outcomes.

Keywords
INTRODUCTION

Ectopic pregnancy (EP), defined as the implantation of a fertilised ovum outside the uterine cavity, remains a major cause of maternal morbidity and mortality, particularly in the first trimester. The reported incidence ranges from 1–2% of all pregnancies, although variation exists depending on diagnostic methods and population risk profiles [1,2]. Despite advances in imaging and biochemical diagnostics, EP continues to present diagnostic and therapeutic challenges for clinicians [3,4].

 

The most common site is the fallopian tube, accounting for over 95% of cases, but ovarian, cervical, and abdominal pregnancies also occur [5]. Classical presentation includes amenorrhoea, abdominal pain, and vaginal bleeding, but these signs are nonspecific, and many women present atypically, leading to delayed or missed diagnosis [6]. Ruptured ectopic pregnancy, in particular, can result in catastrophic haemorrhage, haemodynamic instability, and even maternal death if not recognised promptly [7].

 

A wide range of risk factors for EP has been identified, including pelvic inflammatory disease, prior tubal surgery, use of intrauterine devices (IUDs), assisted reproductive technologies (ART), smoking, and increasing maternal age. The strongest predictors appear to be prior ectopic pregnancy and pre-existing tubal pathology [2,8]. Epidemiological studies have demonstrated that even in the absence of these risk factors, ectopic pregnancy can occur, underscoring the need for high clinical vigilance [4].

 

Advances in diagnostics—particularly the use of transvaginal sonography and serial β-hCG measurements—have greatly improved early recognition of ectopic pregnancy [3]. However, disparities in health-seeking behaviour, healthcare access, and diagnostic resources in different settings continue to affect clinical outcomes [1,4]. In India, where women often present late with ruptured ectopic pregnancies, the burden of morbidity remains high [5].

 

Given this background, the present case–control study was conducted at a tertiary care hospital in Kolkata to evaluate risk factors associated with ectopic pregnancy in the contemporary Indian population. By comparing women with ectopic pregnancies to those with intrauterine pregnancies, this study aimed to clarify the contribution of established and emerging risk factors in this context.

 

Objectives

The primary objective of this study was to identify and evaluate the risk factors associated with ectopic pregnancy among women attending Nilratan Sircar Medical College & Hospital, Kolkata, during the study period (January 2021 to July 2022).

 

The specific objectives were to:

  1. Compare the sociodemographic and reproductive characteristics of women with ectopic pregnancy (cases) and those with intrauterine pregnancy (controls).
  2. Assess the association between prior obstetric and gynaecological history (pelvic inflammatory disease, tubal surgery/sterilisation, infertility, previous ectopic pregnancy) and the occurrence of ectopic pregnancy.
  3. Evaluate the relationship between contraceptive practices, particularly intrauterine device use, and the risk of ectopic pregnancy.
  4. Analyse the clinical presentation and outcomes of women diagnosed with ectopic pregnancy.
MATERIALS AND METHODS

Study Design and Setting

This was a hospital-based prospective case–control study conducted in the Department of Obstetrics and Gynaecology, Nilratan Sircar Medical College and Hospital, Kolkata, between January 2021 and July 2022.

 

Participants

A total of 130 women were included: 65 with confirmed ectopic pregnancy (cases) and 65 with first-trimester intrauterine pregnancy (controls). Cases were recruited consecutively after diagnosis by clinical examination, ultrasonography, and/or intraoperative findings. Controls were selected from antenatal women attending the outpatient department during the same period, matched approximately for age and parity distribution.

 

Inclusion Criteria

  • Cases: Women of reproductive age with confirmed ectopic pregnancy, diagnosed either clinically (history, examination), by transvaginal ultrasonography, or intraoperatively.
  • Controls: Women of reproductive age with viable intrauterine pregnancy (≤12 weeks gestation) confirmed by ultrasonography.

 

Exclusion Criteria

  • Women with haemodynamic instability precluding informed consent.
  • Women with current pelvic inflammatory disease at presentation, where PID was the differential diagnosis.
  • Women with chronic medical illnesses (e.g., cardiac, renal, hepatic, or haematological disorders) likely to confound outcomes.

Note: A past history of pelvic inflammatory disease (PID) was recorded via history-taking and analysed as a potential risk factor. This distinction ensured that only current cases were excluded, while prior episodes were retained for risk factor analysis.

 

Data Collection

Data were collected through structured interviews and medical record review. Variables included:

  • Sociodemographic: Age, education, socioeconomic status (modified Kuppuswamy scale).
  • Reproductive and gynaecological history: Gravidity, parity, prior ectopic pregnancy, pelvic inflammatory disease, infertility, genital tuberculosis, prior dilatation and curettage, tubal sterilisation, and recanalisation procedures.
  • Contraceptive history: Intrauterine device (IUD) use and other methods.
  • Clinical presentation: Amenorrhoea, abdominal pain, vaginal bleeding, shock features.
  • Laboratory parameters: Haemoglobin, haematocrit, blood group.

 

Statistical Analysis

Data were analysed using SPSS (version 26). Continuous variables were summarised as mean ± SD and compared with Student’s t-test. Categorical variables were presented as frequencies and percentages, compared using Chi-square or Fisher’s exact tests as appropriate. Odds ratios (ORs) with 95% confidence intervals (CIs) were calculated for each potential risk factor using univariate logistic regression. For exposures with zero cell counts, the Haldane–Anscombe correction (adding 0.5 to each cell) was applied. Statistical significance was set at p < 0.05.

 

RESULTS
  1. Participant Characteristics

A total of 130 women were included in the study, comprising 65 cases of ectopic pregnancy and 65 controls with intrauterine pregnancy.

 

The age distribution between the two groups did not differ significantly (χ² = 4.29, p = 0.232). The majority of women were in the 26–35-year age group, accounting for 69.2% of cases and 52.2% of controls. Women aged <20 years constituted 7.7% of cases and 9.2% of controls, while those aged >35 years accounted for 7.7% and 15.5%, respectively.

 

Socio-economic status also showed no significant association with ectopic pregnancy (χ² = 0.16, p = 0.921). The upper-lower class predominated in both groups, comprising 46.2% of cases and 43.1% of controls.

Educational status was similarly distributed across groups (χ² = 0.024, p = 0.988). Among cases, 15.4% were illiterate, 41.5% had school-level education, and 24.6% had college-level education. In comparison, 18.5% of controls were illiterate, 46.1% had school education, and 27.7% were college-educated.

                                                                                                                                     
Table 1 presents the baseline sociodemographic characteristics of the study population, and Figure 1 illustrates the age distribution.

 

Table 1: Baseline Characteristics of Cases and Controls

Characteristic

Cases (n=65)

Controls (n=65)

Total (N=130)

p-value

Age group <20 years

5 (7.7%)

6 (9.2%)

11 (8.5%)

0.232*

Age group 21–25 years

10 (15.4%)

15 (23.1%)

25 (19.2%)

 

Age group 26–35 years

45 (69.2%)

34 (52.2%)

79 (60.8%)

 

Age group >35 years

5 (7.7%)

10 (15.5%)

15 (11.5%)

 

Socioeconomic status: Upper lower

30 (46.2%)

28 (43.1%)

58 (44.6%)

0.921*

Socioeconomic status: Lower middle

20 (30.8%)

22 (33.8%)

42 (32.3%)

 

Socioeconomic status: Middle/Upper

15 (23.0%)

15 (23.1%)

30 (23.1%)

 

Education: Illiterate

10 (15.4%)

12 (18.5%)

22 (16.9%)

 

Education: School

27 (41.5%)

30 (46.1%)

57 (43.8%)

0.988*

Education: College

16 (24.6%)

18 (27.7%)

34 (26.1%)

 

2. Clinical Presentation

The predominant presenting symptom among cases was abdominal pain (83.1%), followed by amenorrhoea (46.4%) and bleeding per vaginum (7.9%).By contrast, controls most frequently presented with amenorrhoea (86.7%), and smaller proportions reported nausea (12%) and vomiting (1.3%).

Table 2 summarises the clinical symptoms in cases and controls, and Figure 2 illustrates the distribution of presenting symptoms.

Table 2: Clinical Symptoms of Cases and Controls

Symptoms

Cases (n=65)

Controls (n=65)

Amenorrhea

46.4%

86.7%

Abdominal Pain

83.1%

-

Bleeding P/V

7.9%

-

Nausea

-

12.0%

Vomiting

-

1.3%

  1. Vital Signs and Laboratory Findings

Cases presented with a significantly shorter period of amenorrhoea compared to controls (6.46 ± 1.53 weeks vs 8.47 ± 1.65 weeks; p = 0.043).


The mean pulse rate was also significantly higher in cases (99.95 ± 8.91/min) than in controls (82.58 ± 6.55/min; p = 0.009).No significant differences were observed in systolic or diastolic blood pressure between the two groups (p = 0.102 and p = 0.768, respectively).


The mean haemoglobin concentration was significantly lower among cases (7.08 ± 0.74 g/dL) than controls (8.75 ± 0.81 g/dL; p = 0.009).


Clinical pallor was present in 52.3% of cases, compared with only 3.1% of controls, which was highly significant (p < 0.001).


Table 3 summarises the vital signs and laboratory findings at admission, while Figure 3 presents a comparative view of selected mean parameters.

Table 3: Vital Signs and Laboratory Findings at Admission

Parameter

Cases (n=65)

Controls (n=65)

p-value

Period of Amenorrhoea (weeks)

6.46 ± 1.53

8.47 ± 1.65

0.043 (Sig)

Pulse Rate (/min)

99.95 ± 8.91

82.58 ± 6.55

0.009 (Sig)

Systolic BP (mmHg)

102.77 ± 10.89

104.92 ± 9.36

0.102 (NS)

Diastolic BP (mmHg)

65.69 ± 7.28

66.23 ± 5.19

0.768 (NS)

Haemoglobin (g/dL)

7.08 ± 0.74

8.75 ± 0.81

0.009 (Sig)

Pallor present (%)

52.3%

3.1%

<0.001 (Sig)

  1. Risk Factors Associated with Ectopic Pregnancy

Several reproductive and gynaecological factors were significantly associated with ectopic pregnancy.
A previous history of ectopic pregnancy was reported in 15.4% of cases compared with only 1.5% of controls, corresponding to an odds ratio (OR) of 11.6 (95% CI: 1.4–93.8; p = 0.003).


Pelvic inflammatory disease (PID) was more frequent among cases (27.7% vs 12.3%), with an OR of 2.7 (95% CI: 1.1–6.8; p = 0.029).


Use of an intrauterine device (IUD) was also significantly higher in cases (21.5%) compared to controls (3.1%), with an OR of 8.7 (95% CI: 1.9–39.8; p = 0.001).


Tubal sterilisation was observed in 6.2% of cases and none of the controls, yielding an elevated odds ratio (OR 9.6, 95% CI: 0.5–181.8) though with a very wide confidence interval reflecting small numbers (p = 0.042).

Other factors, including recanalisation (OR 5.2, 95% CI: 0.24–109.6), infertility (OR 1.0, 95% CI: 0.19–5.2), genital tuberculosis (OR 3.0, 95% CI: 0.12–76.2), and history of dilatation and curettage (D&C) (OR 2.8, 95% CI: 0.82–9.4), did not show statistically significant associations.

 

These findings are summarised in Table 4, and illustrated in the forest plot (Figure 4), where the strongest predictors of ectopic pregnancy were prior ectopic pregnancy, IUD use, and history of PID.

 

Table 4 summarises the distribution of risk factors in cases and controls, while Figure 4 presents the odds ratios for significant associations.

Table 4: Risk Factors Associated with Ectopic Pregnancy

Risk factor

Cases (n=65)

Controls (n=65)

OR (95% CI)

p-value

Previous ectopic pregnancy

10 (15.4%)

1 (1.5%)

11.64 (1.44–93.80)

0.003

Pelvic inflammatory disease

18 (27.7%)

8 (12.3%)

2.73 (1.09–6.83)

0.029

IUD use

14 (21.5%)

2 (3.1%)

8.65 (1.88–39.81)

0.001

Tubal sterilisation

4 (6.2%)

0 (0%)

9.59 (0.51–181.76)

0.042*

Recanalisation

2 (3.1%)

0 (0%)

5.16 (0.24–109.55)

0.24

Infertility

3 (4.6%)

3 (4.6%)

1.00 (0.19–5.15)

0.70

Genital tuberculosis

1 (1.5%)

0 (0%)

3.05 (0.12–76.18)

0.31

Dilatation & curettage (D&C)

10 (15.4%)

4 (6.2%)

2.77 (0.82–9.35)

0.10

  1. Maternal Outcomes

Among the 65 women with ectopic pregnancy, 6 (9.2%) presented in shock.
A total of 41 women (63.1%) required blood transfusion during the course of management.
Four women (6.2%) required admission to the Coronary Care Unit (CCU) for intensive monitoring and support. Importantly, no maternal deaths were recorded in this study cohort.
Table 5 provides a summary of the maternal outcomes, and Figure 5 illustrates the frequency distribution of these events.

Table 5: Maternal Outcomes in Women with Ectopic Pregnancy

Outcome

Cases (n=65)

Shock at presentation

6 (9.2%)

Blood transfusion required

41 (63.1%)

CCU admission

4 (6.2%)

Maternal death

0

DISCUSSION

In the present study, we identified several risk factors that significantly increased the odds of ectopic pregnancy, most notably a prior ectopic pregnancy, pelvic inflammatory disease (PID), tubal sterilisation, and intrauterine device (IUD) use. The statistical associations we observed provide important insight into how these risk factors contribute to disease burden in our population.

 

A previous ectopic pregnancy was the strongest risk factor identified, reported in 15.4% of cases compared with only 1.5% of controls. After correcting for odds ratio directionality, this corresponded to an odds ratio of approximately 11.6 (95% CI: 1.44–93.8, p = 0.003). This finding is consistent with the well-established notion that tubal damage from a prior ectopic episode predisposes to recurrence. Menon et al.

 

emphasised the recurrence risk, noting that a prior ectopic pregnancy remains one of the most powerful predictors of future ectopic implantation [9]. Similarly, the European Surgery in Ectopic Pregnancy (ESEP) trial, a multicentre randomised trial, demonstrated that recurrence risk persisted irrespective of whether surgical management was conservative or radical, highlighting that anatomical and functional tubal compromise often remains despite treatment [10]. This evidence collectively underscores the importance of targeted surveillance and preconception counselling for women with prior ectopic gestations.

 

Pelvic inflammatory disease was another significant risk factor in our cohort, present in 27.7% of cases compared with 12.3% of controls, corresponding to an odds ratio of 2.7 (95% CI: 1.1–6.8, p = 0.029). This finding reflects the pathophysiological role of tubal inflammation and scarring, which disrupts ovum transport and predisposes to abnormal implantation. Farquhar’s landmark review similarly concluded that up to one-third of women with PID may subsequently develop tubal factor infertility or ectopic pregnancy due to salpingitis-induced damage [11]. Williams Obstetrics further reinforces this, listing PID as one of the principal contributors to abnormal tubal function [12]. In addition, Fernandez et al. conducted two large case–control studies across multiple centres in France, both of which demonstrated PID to be among the strongest independent predictors of ectopic pregnancy, with effect sizes comparable to those seen in our study [15,16]. The consistency of this association across different populations supports PID as a major modifiable risk factor, particularly relevant in regions with high burden of untreated reproductive tract infections.

 

Tubal sterilisation was also significantly associated with ectopic pregnancy in our study, reported in 6.2% of cases but absent in controls. The corrected odds ratio, calculated with a continuity correction, was 9.6 (95% CI: 0.5–181.8, p = 0.042). Although the confidence interval is wide due to small numbers, the elevated point estimate suggests that sterilisation failure carries a substantial risk of ectopic implantation.

 

 This is biologically plausible: when tubal occlusion fails, residual patency often predisposes to implantation at the occlusion site. Clayton et al. described similar risks, particularly when the sterilisation technique involved fimbrial or mid-tubal segments, which are anatomically more prone to failure [13]. While sterilisation remains a highly effective contraceptive method, these findings highlight the importance of counselling women about the possibility of ectopic pregnancy in the rare event of sterilisation failure.

 

Intrauterine device (IUD) use was another strong predictor, observed in 21.5% of cases compared with 3.1% of controls, with an odds ratio of 8.7 (95% CI: 1.9–39.8, p = 0.001). Although IUDs are highly effective contraceptives, pregnancies that do occur in IUD users are disproportionately more likely to be ectopic. This association is well recognised; Clayton et al. observed that modern contraceptive failure, particularly IUD failure, has become a key contributor to ectopic pregnancy in contemporary practice [14].

 

 Ankum et al., in their meta-analysis, also confirmed significantly increased odds of ectopic pregnancy among IUD users compared to women conceiving without contraception [20]. These findings underscore the importance of early evaluation of pregnancy location in women conceiving with an IUD in situ.

 

Other risk factors, including infertility, recanalisation procedures, genital tuberculosis, and history of dilatation and curettage (D&C), did not demonstrate statistically significant associations in our cohort. Infertility was reported in 4.6% of both groups (OR = 1.0, p = 0.70), suggesting no difference in this study. This differs from findings by Clayton et al. (2022), who reported infertility, particularly due to tubal factors, as a strong independent predictor of ectopic pregnancy [13]. Similarly, recanalisation procedures were uncommon in our series (3.1% vs 0%) and did not achieve statistical significance (OR = 5.2, wide CI crossing unity). Genital tuberculosis, a recognised risk factor in Indian populations due to tubal fibrosis, was reported in only 1.5% of cases and none of the controls, with no significant association. Marion and Meeks, however, emphasised that both genital tuberculosis and uterine instrumentation (such as D&C) can compromise tubal integrity, increasing the risk of abnormal implantation [19]. Our inability to demonstrate significance likely reflects the limited sample size and the low prevalence of these exposures.

 

The corrected forest plot (Figure 4) provides a visual summary of these associations. The strongest predictors—previous ectopic pregnancy, PID, and IUD use—are depicted with confidence intervals that lie entirely above unity, confirming their significance. Tubal sterilisation also demonstrated elevated odds, but the wide interval highlights the imprecision of effect estimates due to small numbers. In contrast, recanalisation, infertility, and genital tuberculosis displayed wide confidence intervals crossing unity, indicating statistical non-significance. Such visualisation is particularly valuable for illustrating both the magnitude and uncertainty of effect estimates in case–control studies, and aligns with modern reporting standards [20].

 

Maternal outcomes in our cohort were favourable, with no maternal deaths recorded. This is encouraging and contrasts with older data. For instance, Creanga et al. reported that ectopic pregnancy contributed significantly to maternal mortality in the United States between 1980 and 2007 [17]. The improved survival in contemporary series such as ours likely reflects advances in early diagnosis, wider availability of transvaginal ultrasound, and sensitive β-hCG assays, as previously described by Farquhar [11,18]. Early surgical and medical interventions, coupled with improved awareness among clinicians, have likely reduced case fatality rates.

 

The age distribution in our study also warrants comment. The clustering of cases in the 26–35-year age group mirrors patterns described by Marion and Meeks, who identified this demographic as particularly vulnerable [19]. This may reflect cumulative reproductive exposures such as contraceptive use, PID, or prior pelvic procedures. Ankum et al.’s meta-analysis further supports this, consolidating evidence that risk factors such as previous ectopic pregnancy, PID, sterilisation, and IUD use are consistently associated with ectopic pregnancy across different populations and age groups [20].

 

In summary, our findings confirm that a history of ectopic pregnancy, PID, tubal sterilisation, and IUD use are significant risk factors for ectopic pregnancy. Other exposures such as infertility, recanalisation, and genital tuberculosis did not achieve significance in our series, but remain biologically plausible contributors supported by prior literature. These results highlight the importance of detailed reproductive history-taking in clinical practice, as well as the potential role of targeted preconception counselling and early pregnancy surveillance in high-risk women.

 

Limitations

This study was limited by its modest sample size, which reduced power to detect associations with less common exposures and resulted in wide confidence intervals. Being hospital-based, the findings may not be generalisable to the wider population. Recall bias from self-reported histories is possible, and odds ratios for rare exposures required continuity corrections, limiting precision. Residual confounding by unmeasured factors such as smoking or assisted reproduction cannot be excluded.

CONCLUSION

Ectopic pregnancy remains a significant cause of maternal morbidity in women of reproductive age. In this hospital-based case–control study, prior ectopic pregnancy, pelvic inflammatory disease, tubal sterilisation, and intrauterine device use emerged as important risk factors. While other factors such as infertility, genital tuberculosis, and uterine instrumentation were observed, they did not reach statistical significance in our cohort. Early recognition of these risk factors is critical to raising clinical suspicion, enabling timely diagnosis, and preventing adverse maternal outcomes. Strengthening preventive strategies, improving reproductive health counselling, and ensuring prompt management remain essential to reducing the burden of ectopic pregnancy.

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