Common Causes of Miscarriage (Before 12 Weeks of Pregnancy)
- Poor Embryonic Cell Division: Leading to miscarriage during the early stages of implantation.
- Natural Selection: A biological defense mechanism where embryos with developmental issues face natural attrition.
- Immunological Factors: Miscarriages triggered by immune imbalances or autoimmune disorders.
- Parental Chromosomal Abnormalities: Resulting in the embryo inheriting chromosomal defects that lead to pregnancy loss.
- Unexplained Factors: Other idiopathic causes.
- Most miscarriages fall into Category 1 or Category 2. In these instances, the pregnancy loss is a biological necessity that cannot—and should not—be artificially prevented. While deeply disheartening, it is an unavoidable natural process.
- If a miscarriage occurs after a gestational sac has been confirmed via ultrasound and a fetal heartbeat has been successfully detected, it is highly likely to fall under Category 2.
The human body possesses an inherent screening system (acting within the first 12 weeks) that naturally terminates a pregnancy when the implanted embryo fails to divide properly, exhibits severe congenital anomalies, or carries chromosomal defects. This natural selection process is statistically more common in cases of severe diminished ovarian reserve or advanced maternal age (40 and older), as the likelihood of developing eggs with chromosomal abnormalities increases.
Consequently, if a patient experiences three or more consecutive miscarriages after a gestational sac has been identified on an ultrasound, gynecologists strongly recommend undergoing a recurrent pregnancy loss (RPL) workup. This evaluation aims to investigate whether the underlying cause stems from Category 3 or Category 4.
- If an immune imbalance or an autoimmune condition (Category 3) is identified, the miscarriage can often be prevented. This is achieved by combining natural conception attempts or IVF cycles with targeted immunotherapy protocols.
Among older patients (aged 37 and above), immunological factors account for a significant portion of repeated implantation failures and miscarriages. As maternal age advances, the immune system becomes more susceptible to dysregulation, often triggered by past viral infections or cumulative environmental factors.
If the issue falls under Category 4, a patient may conceive naturally without difficulty, yet face repetitive miscarriages due to inherited embryonic chromosomal abnormalities. In such scenarios, clinicians strongly advise considering a specialized IVF cycle that incorporates embryonic chromosomal screening prior to transferring the embryo into the uterus.
Furthermore, even if the losses are attributed to Categories 1 and 2, patients who suffer from recurrent miscarriages (three or more losses) are highly encouraged to opt for IVF paired with PGT-A (formerly known as PGS). This specialized procedure allows embryologists to comprehensively screen the chromosomes of each embryo before transfer.
For patients who possess no trouble conceiving naturally but endure repeated miscarriages, undergoing multiple dilation and curettage (D&C) procedures can take a severe toll on reproductive health. The surgical aftermath—such as intrauterine adhesions (Asherman’s syndrome), polyp formation, retained products of conception, and endometrial lining damage—can detrimentally impact future pregnancies. To avoid these compounding risks, fertility specialists actively recommend utilizing specialized PGT-A cycles.
Understanding the Unified Terminology: From PGD/PGS to PGT
The previously separate terms “PGD” and “PGS” have now been unified under the umbrella term PGT (Pre-implantation Genetic Testing). This testing is further categorized into three distinct modalities tailored to the patient’s specific medical history:
- PGT-SR (Pre-implantation Genetic Testing for Structural Rearrangements): Utilized when either partner is a known carrier of a structural chromosomal abnormality (such as translocations or inversions).
- PGT-M (Pre-implantation Genetic Testing for Monogenic/Single-Gene Defects): Formerly known as PGD, this is indicated when either partner carries a specific inheritable genetic disorder or gene mutation.
- PGT-A (Pre-implantation Genetic Testing for Aneuploidy): Formerly known as PGS, this is designed for couples who both possess entirely normal karyotypes but suffer from recurrent miscarriages or unexplained IVF failures due to random chromosomal abnormalities.