What is an ectopic pregnancy
In a normal pregnancy, a fertilized egg travels down the fallopian tube to implant itself in the uterus for further growth and development of the baby. In some abnormal cases, the egg gets implanted somewhere out of the uterus after being fertilized by a sperm . The term ‘ectopic’ stands for ‘out of place’. So, an ectopic pregnancy literally means an out of place pregnancy where the embryo starts growing somewhere other than the uterus. It can occur in the fallopian tubes, the ovary, cervix or directly in your abdomen .
Types of ectopic pregnancy
In a tubal pregnancy the egg implants within the fallopian tube itself instead of finishing its journey to the uterus . It is the most common site for ectopic pregnancy with over 95% of all extra-uterine pregnancies being in the fallopian tube . Tubal pregnancies can be further classified into ampullary , isthmic  and infundibular  ectopic pregnancies, depending on their location, with the first having the highest incidence rate.
Interstitial or Cornual Pregnancy
Also referred to as the interstitial pregnancy, it occurs in the interstitial segment or the part of the fallopian tube lying within the uterine walls . Accounting for 1%-3% of all cases of ectopic pregnancies , it is often quite difficult to detect in the early stages as the implantation usually appears to be within the uterus when viewed on an ultrasound .
Abdominal pregnancy occurs when the implantation happens anywhere in the abdominal cavity instead of the uterus . It can be seen in various unusual places, including around the ovarian ligaments, in the omentum, large vessels, and vital organs as well as in the upper abdominal area (rare cases). It accounts for about 1.4% of all ectopic pregnancies .
In this type of extra-uterine pregnancy, the egg implants itself in the cervix, commonly in the endocervical canal lining [10,11]. One of the rarest forms of extra-uterine pregnancies, its incidence is less than 1% .
An ovarian pregnancy is when the egg implants in the ovary instead of traveling down the fallopian tube to the uterus . Being one of the rarest forms, it accounts for around 1%-3% of ectopic pregnancies .
Caesarean Scar Ectopic Pregnancy
The rarest form of ectopic pregnancy, it happens when the implantation takes place in a cesarean section scar . There are less than 50 recorded cases of ectopic pregnancy in a c-section scar .
In some rare cases (1 out of 4,000 pregnancies), one egg gets implanted normally inside the womb while another may implant itself somewhere outside. This complication is referred to as a heterotopic pregnancy .
Ectopic pregnancy statistics: How common is it
It has an incidence of 1 in every 50 pregnancies in the United States  while 1 out of every 90 pregnancies in the United Kingdom is ectopic .
ICD-9 and ICD-10 codes
The ICD-9 code used for ectopic pregnancy is 633  while its ICD-10 code is O00 .[ref]
- http://www.obgyn.net/tags/ectopic-pregnancy [/ref]