86 Vol 4(2) (2019) 86-90 | jchs-medicine.uitm.edu.my | eISSN 0127-984X https://doi.org/10.24191/jchs.v4i2.7514 INTRODUCTION Heterotopic interstitial pregnancy (HIP) is a diagnosis made when both intrauterine and extrauterine interstitial pregnancy coexist [1]. Heterotopic pregnancy incidence is one in 30,000 naturally conceived pregnancies [2]. With interstitial pregnancy occurrence between 2.4 to 4% of all ectopic pregnancies, the incidence of HIP is said to be exceedingly rare [3-5]. On the other hand, HIP occurs in 80 – 92% of the time following artificial reproductive technology [6, 7]. The consequences of missing the diagnosis of HIP can be disastrous. Maternal mortality associated with interstitial pregnancy ranges from 2 – 2.5% [8]. About 4.8% women died at less than 24 weeks’ gestation as a direct consequence of ectopic pregnancy as reported in Mothers and Babies: Reducing Risk through Audits and Confidential Enquiries across the UK (MBRRACE-UK) report 2016 [9]. The maternal death occurs as a result of massive haemorrhage due to ruptured intramyometrial arcuate vasculature that supply the cornua of uterus occupied by the late diagnosed interstitial pregnancy [4, 9]. Fifty percent of HIP cases have no apparent risk factors, making it difficult to suspect the diagnosis in natural conception based of background risk on its own [5]. In pregnancies conceived via in-vitro fertilisation, background history of previous uni- or bilateral salpingectomy is a significant risk factor that is evident in about 40% of HIP diagnosed in such setting [6]. The use of large embryo transfer medium, relaxed uterus from supraphysiological presence of progesterone released by multiple corpus lutea [10], together with multiple embryo transfer or presence of tubal infertility contribute to the increased risk of HIP in pregnancy conceived via artificial reproductive technology [6]. A third of patients with HIP have no symptom at diagnosis, with remaining 29 – 68% of patients having per vaginal bleeding and/or abdominal pain [7, ABSTRACT Heterotopic interstitial pregnancy in natural conception is very rare. Definitive diagnosis is made by systematic pelvic ultrasound. Simultaneous viable conception observed in both intra- and extra-uterine is pathognomonic of heterotopic interstitial pregnancy. We report a 34-year- old woman primigravida at 10 weeks’ amenorrhoea who underwent evacuation of retained product of conception for missed miscarriage. Intraoperatively, minimal product of conception was retrieved. Bedside pelvic ultrasound showed cystic mass at right superolateral part of uterine fundus suspicious of interstitial pregnancy. Cornual resection was performed via laparotomy. Histopathological examination showed presence of product of conception and interstitial pregnancy. Serum β-human chorionic gonadotropin dropped from 10,027 IU/l on day one post-ERPC to 210 IU/l at day three post-cornual resection. This case report highlighted the challenge in diagnosing heterotopic interstitial pregnancy conceived naturally. Timely diagnosis may avert dire consequences of massive haemorrhage from ruptured uterine cornua. KEYWORDS: Heterotopic interstitial pregnancy; pelvic ultrasound; pelvic magnetic resonance imaging (MRI); cornual resection Received 8 th April 2019 Received in revised form 16 th August 2019 Accepted 17 th September 2019 Corresponding author: Dr. Noor Azura Noor Mohamad Department of Obstetrics and Gynaecology, Faculty of Medicine, Universiti Teknologi MARA Sungai Buloh, Jalan Hospital, 47000 Sungai Buloh, Selangor, Malaysia Email: azuranoor@uitm.edu.my The Challenge in Diagnosing and Managing Heterotopic Interstitial Pregnancy in Natural Conception Noor Azura Noor Mohamad 2, 3 , Suzanna Daud 1, 2 , Sun Ta Thow 3 , Darminder Singh Chopra 3 , Bahiyah Abdullah 1, 2 1 Maternofetal & Embryo (MatE) Research Group, Faculty of Medicine, Universiti Teknologi MARA, Selangor, Malaysia 2 Department of Obstetrics and Gynaecology, Faculty of Medicine, Universiti Teknologi MARA, Selangor, Malaysia 3 Department of Obstetrics and Gynaecology, Hospital Sungai Buloh, Selangor, Malaysia