algorithm of the management of a pregnancy of unknown location, that is, a positive pregnancy test but no pregnancy is found on transvaginal ultrasonography. if serum hcg at 0 hours is more than 1000 iu/l and there is no history suggestive of complete miscarriage, the ultrasonography should be repeated as soon as possible. where no intrauterine pregnancy (iup) is seen on ultrasound, measuring β-human chorionic gonadotropin (β-hcg) levels may aid in the diagnosis. the rationale is that a low β-hcg level may indicate that the pregnancy is intrauterine but yet too small to be visible on ultrasonography. while some physicians consider that the threshold where an intrauterine pregnancy should be visible on transvaginal ultrasound is around 1500 miu/ml of β-hcg, a review in the jama rational clinical examination series showed that there is no single threshold for the β-human chorionic gonadotropin that confirms an ectopic pregnancy. instead, the best test in a pregnant woman is a high resolution transvaginal ultrasound. the presence of an adnexal mass in the absence of an intrauterine pregnancy on transvaginal sonography increases the likelihood of an ectopic pregnancy 100-fold (lr+ 111). when there are no adnexal abnormalities on transvaginal sonography, the likelihood of an ectopic pregnancy decreases (lr- 0.12). an empty uterus with levels higher than 1500 miu/ml may be evidence of an ectopic pregnancy, but may also be consistent with an intrauterine pregnancy which is simply too small to be seen on ultrasound. if the diagnosis is uncertain, it may be necessary to wait a few days and repeat the blood work. this can be done by measuring the β-hcg level approximately 48 hours later and repeating the ultrasound. the serum hcg ratios and logistic regression models appear to be better than absolute single serum hcg level. if the β-hcg falls on repeat examination, this strongly suggests a spontaneous abortion or rupture. the fall in serum hcg over 48 hours may be measured as the hcg ratio, which is calculated as: h c g r a t i o = h c g a t 48 h h c g a t 0 h an hcg ratio of 0.87, that is, a decrease in hcg of 13% over 48 hours, has a sensitivity of 93% and specificity of 97% for predicting a failing pregnancy of unknown location (pul). the majority of cases of ectopic pregnancy will have serial serum hcg levels that increase more slowly than would be expected with an iup (that is, a suboptimal rise), or decrease more slowly than would be expected with a failing pul. however, up to 20% of cases of ectopic pregnancy have serum hcg doubling times similar to that of an iup, and around 10% of ep cases have hcg patterns similar to a failing pul. direct examination a laparoscopy or laparotomy can also be performed to visually confirm an ectopic pregnancy. this is generally reserved for women presenting with signs of an acute abdomen and hypovolemic shock. often if a tubal abortion or tubal rupture has occurred, it is difficult to find the pregnancy tissue. a laparoscopy in very early ectopic pregnancy rarely shows a normal-looking fallopian tube. culdocentesis culdocentesis, in which fluid is retrieved from the space separating the vagina and rectum, is a less commonly performed test that may be used to look for internal bleeding. in this test, a needle is inserted into the space at the very top of the vagina, behind the uterus and in front of the rectum. any blood or fluid found may have been derived from a ruptured ectopic pregnancy. progesterone levels progesterone levels of less than 20 nmol/l have a high predictive value for failing pregnancies, whilst levels over 25 nmol/l are likely to predict viable pregnancies, and levels over 60 nmol/l are strongly so. this may help in identifying failing pul that are at low risk and thereby needing less follow-up. inhibin a may also be useful for predicting spontaneous resolution of pul, but is not as good as progesterone for this purpose. mathematical models there are various mathematical models, such as logistic regression models and bayesian networks, for the prediction of pul outcome based on multiple parameters. mathematical models also aim to identify puls that are low risk, that is, failing puls and iups. dilation and curettage dilation and curettage (d&c) is sometimes used to diagnose pregnancy location with the aim of differentiating between an ep and a non-viable iup in situations where a viable iup can be ruled out. specific indications for this procedure include either of the following: no visible iup on transvaginal ultrasonography with a serum hcg of more than 2000 miu/ml. an abnormal rise in hcg level. a rise of 35% over 48 hours is proposed as the minimal rise consistent with a viable intrauterine pregnancy. an abnormal fall in hcg level, such as defined as one of less than 20% in two days. tubal pregnancy the vast majority of ectopic pregnancies implant in the fallopian tube. pregnancies can grow in the fimbrial end (5% of all ectopic pregnancies), the ampullary section (80%), the isthmus (12%), and the cornual and interstitial part of the tube (2%). mortality of a tubal pregnancy at the isthmus or within the uterus (interstitial pregnancy) is higher as there is increased vascularity that may result more likely in sudden major internal bleeding. a review published in 2010 supports the hypothesis that tubal ectopic pregnancy is caused by a combination of retention of the embryo within the fallopian tube due to impaired embryo-tubal transport and alterations in the tubal environment allowing early implantation to occur. nontubal ectopic pregnancy two percent of ectopic pregnancies occur in the ovary, cervix, or are intra-abdominal. transvaginal ultrasound examination is usually able to detect a cervical pregnancy. an ovarian pregnancy is differentiated from a tubal pregnancy by the spiegelberg criteria. while a fetus of ectopic pregnancy is typically not viable, very rarely, a live baby has been delivered from an abdominal pregnancy. in such a situation the placenta sits on the intra-abdominal organs or the peritoneum and has found sufficient blood supply. this is generally bowel or mesentery, but other sites, such as the renal (kidney), liver or hepatic (liver) artery or even aorta have been described. support to near viability has occasionally been described, but even in third world countries, the diagnosis is most commonly made at 16 to 20 weeks' gestation. such a fetus would have to be delivered by laparotomy. maternal morbidity and mortality from extrauterine pregnancy are high as attempts to remove the placenta from the organs to which it is attached usually lead to uncontrollable bleeding from the attachment site. if the organ to which the placenta is attached is removable, such as a section of bowel, then the placenta should be removed together with that organ. this is such a rare occurrence that true data is unavailable and reliance must be made on anecdotal reports. however, the vast majority of abdominal pregnancies require intervention well before fetal viability because of the risk of bleeding. with the increase in cesarean sections performed worldwide, cesarean section ectopic pregnancies (csp) are rare, but becoming more common. the incidence of csp is not well known, however there have been estimates based on different populations of 1:1800–1:2216. csp are characterized by abnormal implantation into the scar from a previous cesarean section, and allowed to continue can cause serious complications such as uterine rupture and hemorrhage. patients with csp generally present without symptoms, however symptoms can include vaginal bleeding that may or may not be associated with pain. the diagnosis of csp is made by ultrasound and four characteristics are noted: (1) empty uterine cavity with bright hyperechoic endometrial stripe (2) empty cervical canal (3) intrauterine mass in the anterior part of the uterine isthmus, and (4) absence of the anterior uterine muscle layer, and/or absence or thinning between the bladder and gestational sac, measuring less than 5 mm. given the rarity of the diagnosis, treatment options tend to be described in case reports and series, ranging from medical with methotrexate or kcl to surgical with dilation and curettage, uterine wedge resection, or hysterectomy. a double-balloon catheter technique has also been described, allowing for uterine preservation. recurrence risk for csp is unknown, and early ultrasound in the next pregnancy is recommended. heterotopic pregnancy main article: heterotopic pregnancy in rare cases of ectopic pregnancy, there may be two fertilized eggs, one outside the uterus and the other inside. this is called a heterotopic pregnancy. often the intrauterine pregnancy is discovered later than the ectopic, mainly because of the painful emergency nature of ectopic pregnancies. since ectopic pregnancies are normally discovered and removed very early in the pregnancy, an ultrasound may not find the additional pregnancy inside the uterus. when hcg levels continue to rise after the removal of the ectopic pregnancy, there is the chance that a pregnancy inside the uterus is still viable. this is normally discovered through an ultrasound. although rare, heterotopic pregnancies are becoming more common, likely due to increased use of ivf. the survival rate of the uterine fetus of a heterotopic pregnancy is around 70%. rudimentary horn pregnancy main article: rudimentary horn pregnancy a pregnancy in a rudimentary horn refers to a rare and life-threatening condition that occurs when a fertilized egg implants inside the small rudimentary horn of a unicornuate uterus, which is a type of congenital uterine abnormality caused by the incomplete development of one of the müllerian ducts. this type of ectopic pregnancy is often results in rupture of the rudimentary horn between 10 and 15 weeks of gestation, leading to a high risk of morbidity and mortality. persistent ectopic pregnancy a persistent ectopic pregnancy refers to the continuation of trophoblastic growth after a surgical intervention to remove an ectopic pregnancy. after a conservative procedure that attempts to preserve the affected fallopian tube such as a salpingotomy, in about 15–20% the major portion of the ectopic growth may have been removed, but some trophoblastic tissue, perhaps deeply embedded, has escaped removal and continues to grow, generating a new rise in hcg levels. after weeks this may lead to new clinical symptoms including bleeding. for this reason hcg levels may have to be monitored after removal of an ectopic pregnancy to assure their decline, also methotrexate can be given at the time of surgery prophylactically. pregnancy of unknown location pregnancy of unknown location (pul) is the term used for a pregnancy where there is a positive pregnancy test but no pregnancy has been visualized using transvaginal ultrasonography. specialized early pregnancy departments have estimated that between 8% and 10% of women attending for an ultrasound assessment in early pregnancy will be classified as having a pul. the true nature of the pregnancy can be an ongoing viable intrauterine pregnancy, a failed pregnancy, an ectopic pregnancy or rarely a persisting pul. because of frequent ambiguity on ultrasonography examinations, the following classification is proposed: conditioncriteria definite ectopic pregnancyextrauterine gestational sac with yolk sac or embryo (with or without cardiac activity). pregnancy of unknown location – probable ectopic pregnancyinhomogeneous adnexal mass or extrauterine sac-like structure. "true" pregnancy of unknown locationno signs of intrauterine nor extrauterine pregnancy on transvaginal ultrasonography. pregnancy of unknown location – probable intrauterine pregnancyintrauterine gestational sac-like structure. definite intrauterine pregnancyintrauterine gestational sac with yolk sac or embryo (with or without cardiac activity). in women with a pregnancy of unknown location, between 6% and 20% have an ectopic pregnancy. in cases of pregnancy of unknown location and a history of heavy bleeding, it has been estimated that approximately 6% have an underlying ectopic pregnancy. between 30% and 47% of women with pregnancy of unknown location are ultimately diagnosed with an ongoing intrauterine pregnancy, whereof the majority (50–70%) will be found to have failing pregnancies where the location is never confirmed. chorionic villus on histopathological examination of a tubal pregnancy persisting pul is where the hcg level does not spontaneously decline and no intrauterine or ectopic pregnancy is identified on follow-up transvaginal ultrasonography. a persisting pul is likely either a small ectopic pregnancy that has not been visualized, or a retained trophoblast in the endometrial cavity. treatment should only be considered when a potentially viable intrauterine pregnancy has been definitively excluded. a treated persistent pul is defined as one managed medically (generally with methotrexate) without confirmation of