During Week 2, major abnormalities of the blastocyst in general result in failure to implant or spontaneous abortion.
A second major class of abnormality occurs when the blastocyst "hatches" either too early or in the incorrect place, resulting in an ectopic pregnany. If implantation occurs too early, then implantation can occur in the uterine tube which is also called a tubal pregnancy.
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Tubal Pregnancy |
Hydatidiform Mole |
Another type of abnormality is when only the conceptus trophoblast layers proliferates and not the embryoblast, no embryo develops, this is called a hydatidiform mole which is due to the continuing presence of the trophoblastic layer, this abnormal conceptus can also implant in the uterus. Prenatal diagnosis by ultrasound analysis demonstrates the absence of a embryo.
Page Links: Introduction | Some Recent Findings | Self Assessment Questions | Ectopic Implantation | Tubal Pregnancy | Hydatidiform mole | References | Glossary
Güney M, Erdemoglu E, Oral B, Karahan N, Mungan T. Leukemia inhibitory factor (LIF) is immunohistochemically localized in tubal ectopic pregnancy. Acta Histochem. 2008 Feb 6;
Piura B, Rabinovich A, Hershkovitz R, Maor E, Mazor M. Twin pregnancy with a complete hydatidiform mole and surviving co-existent fetus. Arch Gynecol Obstet. 2008 Feb 14;
"Twin pregnancy with complete hydatidiform mole and co-existent fetus (CHMF) resulting in a healthy take-home baby is rare, with only 30 cases documented in detail in the literature. Continuation of a twin pregnancy with CHMF is an acceptable option ...an increased risk of developing pre-eclampsia and fetal loss due to miscarriage. The chance of a live term birth is less than 50% with nearly 33% of the mothers developing persistent gestational trophoblastic disease after delivery."
Seeber BE, Barnhart KT. Suspected ectopic pregnancy. Obstet Gynecol. 2006 Feb;107(2 Pt 1):399-413. Review. Erratum in: Obstet Gynecol. 2006 Apr;107(4):955.
"Women who present with pain and bleeding in the first trimester are at risk for ectopic pregnancy, a life-threatening condition. Conditions that predispose a woman to ectopic pregnancy are damaged fallopian tubes from prior tubal surgery or previous pelvic infection, smoking, and conception using assisted reproduction. Many women without risk factors can develop an ectopic pregnancy."
"Ectopic pregnancy is a high-risk condition that occurs in 1.9 percent of reported pregnancies." (More? Lozeau AM, Potter B., 2005)
Abnormal ectopic implantation occurs at all sites that are not within the uterine cavity. These implantation sites include within the uterine tube (also called Tubal Pregnancy) and outside the uterus within the peritoneal cavity.
Recent findings suggest that in tubal ectopic pregnancy expression of similar factors (LIF) occurs as in those seen in normal uterine implantation sites (More? LIF in tubal ectopic pregnancy).
Ectopic Pregnancy (Historic image)
The most common form of ectopic pregnancy is Tubal Pregnancy when implantation begins before the blastocyst has reached the uterine cavity. (More? Tubal Pregnancy)
The less frequent form of ectopic pregnancy occurs when the blastocyst never enters the uterus and remains in the peritoneal cavity. In this second case implanation can occur on any structure within the peritoneal cavity including: ovary, external surface of the uterus, bladder, bowel, mesentry or peritoneal wall.
Links: Medline Plus - Ectopic pregnancy
Historic image: Reinier de Graaf (1641-1673), a Dutch physician who studied pregnancy in rabbits, copied this image from an earlier French publication.
The most common form of ectopic pregnancy is tubal pregnancy when implantation begins before the blastocyst has reached the uterine cavity within the uterine tube (uterine horn, fallopian tube).
Recent findings suggest that in tubal ectopic pregnancy expression of similar factors (LIF) occurs as in those seen in normal uterine implantation sites (More? LIF in tubal ectopic pregnancy). The implantation site means that the conceptus is not shed during the normal menstral cycle. In addition, implantation allows early placental development, secretion of hCG, and maintainance of the corpus luteum. Maternally this establishes the same features of a normal pregnancy and the embryo may also complete the early embryonic stages of development.
Implantation within the tube can often be detected by ultrasound techniques (More? Abnormal Ultrasound - Tubal Pregnancy).
Tubal pregnancy, embryo approx Carnegie stage 17
Embryo implants and begins developing prematurely in the fallopian tube (uterine horn). Image shows surgically removed, formalin-fixed fallopian tube which has been opened to reveal human embryo and placenta. (approx Carnegie stage 17, embryo cr length 0.95cm)
(Image source: CDC/Dr. Edwin P. Ewing, Jr., 1972 Link to original image)
Several forms of hydatidiform mole: partial mole, complete mole and persistent gestational trophoblastic tumor. (More? mole types). Many of these tumours arise from a haploid sperm fertilizing an egg without a female pronucleus (the alternative form, an embryo without sperm contribution, is called parthenogenesis). The tumour has a "grape-like" placental appearance without enclosed embryo formation. Following a first molar pregnancy, there is approximately a 1% risk of a second molar pregnancy.
Hydatidiform Mole (Image: ACT Pathology description)
ACT Pathology Description
"Macroscopic: The specimen is an enlarged uterus (140x140x100mm, weighing 725g) with right and left ovaries and fallopian tubes attached. Opening the uterus shows a cavity filled with a grape-like mass. The wall of the uterus is thickened and fibrous.
Microscopic: The sections show an interlacing structure within the fibrous lesion. Sections of the cystic contents show numerous dilated and mucoid degenerate proliferative chorionic villi."
(More? ACT Pathology - Uterus benign fibromyoma hydatidiform mole)
Types
Complete mole - chromosomal genetic material from the ovum (egg) is lost, by an unknown process. Fertilization then occurs with one or two sperm and an androgenic (from the male only) conceptus (fertilized egg) is formed. With this conceptus the embryo (fetus, baby) does not develop at all but the placenta does grow but it is abnormal and forms lots of cysts and has no blood vessels. These cysts look like a cluster of grapes and that is why it is called a hydatidiform mole (grape like). A hydatidiform mole miscarries by about 16 to 18 weeks gestational age. Since the diagnosis can be made by ultrasound before that time, it is better for you to have an evacuation of the uterus (D & C) so that there is no undue bleeding and no infection. Human chorionic gonadotropin (hCG) will assist in making the diagnosis.
Partial mole - three sets of chromosomes instead of the usual two and this is called triploidy. With such a pregnancy the chromosomal (genetic) material from the ovum (egg) is retained and the egg is fertilized by one or two sperm. Since with partial mole there are maternal chromosomes there is a fetus but because of the three sets of chromosomes this fetus is always grossly abnormal and will not survive. (Text modified from: International Society for the Study of Trophoblastic Diseases,see also JRM Gestational Trophoblastic Disease)
Tumour Growth
Like any tumour, unless removed there is a risk of progression:
Stage I: Tumor confined to uterus (non-metastatic)
Stage II: Tumor involving pelvic organs and/or vagina
Stage III: Tumor involving lungs, with or without involving pelvic structures and/or vagina
Stage IV: Tumor involving distant organs
Placental Mesenchymal Dysplasia due to a similar "grape-like" placental appearance, this rare disorder has been mistaken both clinically and macroscopically for a partial hydatidiform molar pregnancy. This disorder also has a high incidence of intrauterine growth restriction (IUGR) and fetal death. (More? Placenta Development- Abnormalities)
Twin Pregnancy Mole - hydatidiform mole and co-existent healthy fetus is a very rare (only 30 cases documented in detail in the literature). Piura B, Rabinovich A, Hershkovitz R, Maor E, Mazor M. Twin pregnancy with a complete hydatidiform mole and surviving co-existent fetus. Arch Gynecol Obstet. 2008 Feb 14;
Links: International Society for the Study of Trophoblastic Diseases | Sydney Gynaecological Oncology Group Gestational Trophoblastic Disease | ACT Pathology Uterus benign fibromyoma hydatidiform mole | The Journal of Reproductive Medicine Gestational Trophoblastic Disease (1998) Dana-Farber Cancer Institute Gynecologic Oncology Program
Links: Journals | Online Textbooks | Search Textbooks | PubMed | Search PubMed | Glossary
Search NLM Online Textbooks: ectopic pregnancy | hydatidiform mole
Reviews
Seeber BE, Barnhart KT. Suspected ectopic pregnancy. Obstet Gynecol. 2006 Feb;107(2 Pt 1):399-413. Review. Erratum in: Obstet Gynecol. 2006 Apr;107(4):955.
Lozeau AM, Potter B. Diagnosis and management of ectopic pregnancy. Am Fam Physician. 2005 Nov 1;72(9):1707-14. Review. Summary for patients in: Am Fam Physician. 2005 Nov 1;72(9):1719-20.
Güney M, Erdemoglu E, Oral B, Karahan N, Mungan T. Leukemia inhibitory factor (LIF) is immunohistochemically localized in tubal ectopic pregnancy. Acta Histochem. 2008 Feb 6;
Niemann I, Hansen ES, Sunde L. The risk of persistent trophoblastic disease after hydatidiform mole classified by morphology and ploidy. Gynecol Oncol. 2007 Feb;104(2):411-5.
Yoon SJ, Kim KH, Chung HM, Choi DH, Lee WS, Cha KY, Lee KA. Gene expression profiling of early follicular development in primordial, primary, and secondary follicles. Fertil Steril. 2006 Jan;85(1):193-203.
Search PubMed
Search April 2006 "ectopic pregnancy" 11990 reference articles of which 996 were reviews.
Search PubMed: term= ectopic pregnancy | tubal pregnancy | hydatidiform mole
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Week 2 is about blastocyst "hatching", implantation and bilaminar embryo development.
There are two major abnormalities that may become evident at this time, ectopic pregnancy and hydatidiform mole. Niether of these conditions can, and will not, proceed to term and generally require medical intervention.
A large number of abnormal conceptuses will be spontaneously aborted at this stage and a normal menstral cycle may also occur.
Please email Dr Mark Hill if you wish to make a comment about this current project.