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The transformation of a single cell into a complex multicellular organism is an intricate, fascinating process, entailing a series of rapid cell divisions and differentiation. The second and third weeks of embryological development are crucial, involving the implantation of the blastocyst into the uterine wall; the establishment of three distinct germ layers - the mesoderm, endoderm and ectoderm - through gastrulation; and encompass the beginnings of the neurulation process, resulting in central nervous system (CNS) development and neural tube formation. Abnormal blastocyst implantation may cause in ectopic pregnancy, hydatidiform mole or gestational trophoblastic diseases, while defects in primary neurulation are implicated in anencephaly, spina bifida, and craniorachischisis.

Hydatidiform mole, or molar pregnancy, is the most common of the pathologies that come under gestational trophoblastic disease. It categorizes by a non-viable fertilized egg implanting into the uterine wall, causing abnormal and excessive proliferation of placental tissue. The moles can be either complete or partial. A complete mole forms when an oocyte with no female chromosomes is fertilized by single sperm, which then duplicates its chromosomes via endoreplication to form a diploid embryo composed only of paternal chromosomes. This mechanism occurs in approximately 80% of complete molar pregnancies, with the remaining 20% formed when the empty oocyte becomes fertilized by two sperm [5]. As the embryo is unable to develop due to the lack of maternal chromosomes, it leads to the uncontrolled proliferation of the syncytiotrophoblast creating an abnormal placental mass with distended chorionic villi. Partial molar pregnancies are less common than complete molar pregnancies and occur when a normal egg is fertilized by two sperm, thus creating an embryo with 69 chromosomes. The cytotrophoblast layer undergoes proliferation in partial moles which will form both normal and distended chorionic villi. Unlike complete moles, a fetus will begin to develop. However, there will be multiple defects and abnormalities, leading to a spontaneous abortion usually within the first trimester. Although both complete and partial moles will usually miscarry without intervention, there is a risk of the masses developing into choriocarcinoma if they do not get removed. Neural tube defects are the second commonest group of birth abnormalities worldwide following congenital heart diseases and exist on a vast clinical severity spectrum. Open lesions, such as anencephaly and craniorachischisis, are generally incompatible with life and are caused by a failure of the neural tube to close properly, thereby exposing the neural folds to amniotic fluid, while the least severe stem from secondary neuralation abnormalities, and have the name of spinal dysraphism. In these instances, there is no evidence of failed neural tube closure; instead, such pathologies are attributable to abnormal development of the cranial mesoderm.