Interstitial implantation of fertilized ovum is completed on the?

Appeared in: UPRVUNL - 2021

Explanation

Interstitial implantation is the process where the blastocyst deeply embeds itself into the uterine wall.
This process is considered complete when the blastocyst is fully covered by the endometrial epithelium.
According to embryological timelines, this event is finished by the 10th or 11th day after fertilization, making the 11th day the correct answer.
By this time, the developing placenta begins to produce detectable levels of hCG.

Option A: On the 2nd day after fertilization, the conceptus is a zygote undergoing cleavage divisions and is still located in the fallopian tube, far from the uterus.
Option B: The 6th day marks the beginning of implantation, when the blastocyst first makes contact with and adheres to the uterine wall (apposition and adhesion phases).
Option D: The 7th day is part of the initial phase of implantation. The blastocyst begins to invade the endometrium, but it is not yet fully embedded.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Timeline of fertilized ovum implantation as background academic context rather than a clinical decision trigger.
The completion of implantation is clinically significant as it marks the point when the syncytiotrophoblast produces enough human chorionic gonadotropin (hCG) to be detected in maternal blood, allowing for early pregnancy confirmation.
Understanding this timeline is crucial for assisted reproductive technologies like IVF. It defines the 'window of implantation' (days 20-24 of a typical menstrual cycle), the period when the endometrium is most receptive to an embryo.
What if? If implantation occurs outside the normal uterine location (e.g., in the fallopian tube), it results in an ectopic pregnancy. This is a medical emergency because the growing embryo can rupture the tube, causing severe internal bleeding.

How to Approach the Question

First, identify the key terms in the question: 'interstitial implantation' and 'completed'.
Recognize that this is a factual recall question about a specific physiological timeline in early pregnancy.
Mentally review the sequence of events: fertilization, travel through the fallopian tube, entry into the uterus, and then implantation.
Crucially, differentiate between the initiation of implantation (which starts around day 6-7) and its completion.
Eliminate options that are clearly too early (2nd day) or represent the beginning of the process (6th and 7th days).
Select the option that corresponds to the time when the blastocyst is fully embedded and covered by the uterine lining, which is around day 10-11.

Concept Tested & Keywords

Q3WDHaBbC5vc6mGhn3LUiB

E6 Obstetrics Williams pp. 64-86, 63-85

Practise the full UPRVUNL - 2021

Attempt every question from this paper in a timed mock, then review the full solution for each one.