There is no specific time frame that all ectopic pregnancies are destined to rupture and neither is there a formula to predict when a particular ectopic pregnancy will rupture. Therefore prompt management must be taken whenever an unruptured ectopic pregnancy is detetced in pegnancy during a routine ultrasound scan to prevent a complication. However various factors may contribute to how early or late a particular ectopic pregnancy may rupture. Remember, the fallopian tube is not meant primarily for the nourishment and nurturing of a fetus or baby for long, rather, its purpose is to serve as a conduit for sperms to swim to the ovum or egg prior to fertilization and to convey the newly formed embryo after fertilzation back to the womb in the earliest days following concepton. A few of the factors that may contribute to early or late rupture of an ectopic pregnancy are:
1) The portion of the fallopian tube in which the ectopic pregnancy implants: Because different portions of the fallopian tubes have different diameters and thickness, the site of implantation of the fallopian tube may influence how early or late the fallopian tube ruptures. In general, the diameter of the portion of the fallopian tube in which the embryo implants is directly related to how long it will take the fallopian tube to rupture. While the diameter of the fallopian tube is generally known to be less than 1 cm, its diameters varies depending on different parts of the fallopian tube, e.g. at the isthmus, the diameter is about 2 to 3 mm and at the ampulla, the diameter is about 6 mm. Hence, an ectopic pregnancy implanting in the isthmus is more likely to rupture earlier (about 4 to 6 weeks from the LMP) than that implanting in the ampulla (widest portion of the fallopian tube which usually takes about 6 to 8 weeks to rupture). This is not exactly so for an interstitial ectopic pregnancy which although implants in the interstitium which is the portion of the fallopian tube with the smallest diameter (about 0.5mm), it ruptures much more later than any other parts of the fallopian tube, thanks to its much thicker wall; it is the only portion of the fallopian tube that is surrounded by the uterine muscles. As a rule of thumb, the thicker the wall of an ectopic pregnancy, the more distensible the tube can get before it ruptures. Hence, an interstitial ectopic may remain unruptured until 12 to 14 weeks of pregnancy, way much later than any other tubal ectopic pregnancies. This also goes for all other non tubal ectopic pregnancies (see: DEFINITIONS AND TYPES OF ECTOPIC PREGNANCIES), that exist in the womb or abdomen which becuase of their relatively thicker wall are able to distend to a much larger diameter as the fetus grows and also rupture much later than those in the fallopian tubes.
2) The viability (being alive) and the rate of growth of an ectopic pregnancy also contributes to the risk of rupture of an ectopic pregnancy. Occasionally, an ectopic pregnancy with no heart beat, may be seen in a woman during a routine ultrasound scan who presents only with symptoms of early pregnancy for an ultrasound examination. This is referred to as a non viable ectopic pregnancy, i.e. a lifeless ectopic pregnancy. This type of ectopic pregnancy has no potential to grow nor to expand. On the other hand, a viable ectopic i.e. one in which the fetal heart activity is seen on ultrasound, has a tendency to grow, expand and a higher chance of rupture compared to a non viable ectopic pregnancy. Therefore, regardless of location, the risk of rupture of an ectopic pregnancy is increased in a viable ectopic pregnancy than a non viable ectopic pregnancy. However, even a non viable ectopic pregnancy can still rupture as time goes on. Remember the internal diameter of a fallopian tube is just about 0.5mm to 1mm and an ectopic pregnancy may distend the tube up to about 4 to 5 cm (6 to 20 times that of the normal diameter) depending on the distensibility of the fallopian tube, before it ruptures.
3) Another hypothetical factor that may increase the chance of rupture of a non suspected ectopic pregnancy includes the presence of strenous physical activities. These external factors may further exert some stress on the already fragile wall of an ectopic pregnancy.
Therefore, it is obvious that various factors may influence the timing of rupture of an ectopic pregnancy and as such, it is quite unpredictable to determine when an ectopic pregnancy will rupture. But as I always advise, because ectopic pregnancy occurs only in 2 to 3% of all pregnancies whether planned or unplanned, because there are little or no way of predicting who will be affected, it is important that all women who are sexually active should do a pregnancy test once they miss their periods and follow it up with a transvaginal ultrasound scan if positive, to determine the location and viability of the pregnancy as early as possible. This is because even though ruptured ectopic pregnancies are rare before 5 weeks of getting pregnant, it is still possible to have a ruptured ectopic pregnancy by the 5th week of pregnancy. For more information, kindly CHAT WITH OUR CONSULTANTS.