The testes typically descend into the scrotum between 28 and 35 weeks of gestation during fetal development.
The Crucial Journey: Understanding Testicular Descent
The descent of the testes is a vital step in male fetal development. This process ensures that the testes move from their original location inside the abdomen to their final position within the scrotum. This migration is essential for proper sperm production and overall male fertility later in life. Without this descent, conditions such as cryptorchidism—where one or both testes fail to descend—can occur, potentially leading to complications like infertility or increased cancer risk.
The testes initially form near the kidneys during early embryonic stages. Over time, they travel down through the inguinal canal into the scrotal sac, guided by a fibrous structure known as the gubernaculum. The timing of this journey is tightly regulated by hormonal and mechanical factors within the fetus.
Stages of Testicular Descent
Testicular descent happens in two main phases: the transabdominal phase and the inguinoscrotal phase. Each phase involves different mechanisms and occurs at distinct times during gestation.
Transabdominal Phase
This first phase occurs roughly between weeks 8 and 15 of gestation. During this stage, the testes move from their initial position near the kidneys down to the internal inguinal ring, which marks the entrance to the inguinal canal. The gubernaculum plays a crucial role here by shortening and pulling the testes downward.
Hormones like insulin-like peptide 3 (INSL3), secreted by Leydig cells in the testes, are critical in this phase. INSL3 promotes gubernacular growth and thickening, creating a path for descent. Additionally, anti-Müllerian hormone (AMH) influences regression of female reproductive structures but also indirectly supports testicular positioning.
Inguinoscrotal Phase
This second phase spans approximately from week 25 to birth (around week 40). The testes pass through the inguinal canal into the scrotum itself. Unlike the transabdominal phase, this stage is heavily reliant on androgen hormones, particularly testosterone.
Testosterone stimulates migration of nerve fibers and smooth muscle contractions that help guide the testes through the canal. The gubernaculum continues to shorten and pull downward until it reaches its final attachment point inside the scrotum.
This phase culminates with complete descent usually between weeks 28 and 35, although some variation exists among individuals.
Hormonal Control Behind Testicular Descent
Hormones are central players in regulating when and how testes descend into their proper place. Two main hormonal players dominate this process: INSL3 and testosterone.
INSL3 initiates early gubernacular development in the transabdominal phase. Without sufficient INSL3 signaling, testicular descent may stall early on.
Testosterone, produced by fetal Leydig cells starting around week 8-10, takes over in later stages. It ensures proper migration through the inguinal canal by inducing nerve growth and muscular changes needed for movement.
Disruptions in hormone production or receptor function can cause incomplete or delayed descent. For example, mutations affecting INSL3 or androgen receptors have been linked to cryptorchidism cases.
Anatomical Structures Involved in Descent
Several key anatomical components work together to enable testicular descent:
- Gubernaculum: A ligamentous cord connecting each testis to future scrotal skin; it shortens during descent.
- Inguinal Canal: A passageway through which testes migrate from abdomen to scrotum.
- Processus Vaginalis: An outpouching of peritoneum that precedes testicular descent; it normally closes after birth.
- Spermatic Cord: Contains blood vessels, nerves, lymphatics supporting testis during migration.
Failure or abnormalities in any of these structures can impede normal descent or cause complications such as hernias or hydroceles.
The Timing: When Do Testes Descend Into Scrotum?
Pinpointing exactly when testes descend can vary slightly but generally follows a consistent timeline:
| Gestational Age (Weeks) | Event | Description |
|---|---|---|
| 8-15 | Transabdominal Phase | Testes move from near kidneys toward internal inguinal ring under INSL3 influence. |
| 25-28 | Start Inguinoscrotal Phase | Testes begin passing through inguinal canal into scrotum driven by testosterone. |
| 28-35 | Main Descent Window | Majority of fetuses complete testicular descent into scrotum during this period. |
| 36-40 (Birth) | Late Descent & Final Positioning | A small percentage finish descent close to birth; postnatal descent is rare but possible. |
Most male infants will have fully descended testes at birth or shortly thereafter. In about 3% of full-term newborns, one or both testes may still be undescended but often descend within a few months after birth naturally.
The Importance of Proper Testicular Positioning
Why does it matter when and where testes settle? The scrotum provides an environment cooler than core body temperature—typically about 2–4°C lower—which is crucial for spermatogenesis (sperm production). If testes remain inside the warmer abdomen, sperm development can be impaired.
Undescended testes increase risks for several health issues:
- Cancer Risk: Cryptorchidism is associated with higher risk of testicular cancer later in life.
- Infertility: Improper temperature regulation can reduce sperm count and quality.
- Torsion Risk: Undescended testes are more prone to twisting on their blood supply causing acute pain.
- Psychosocial Impact: Visible absence or asymmetry may affect self-esteem during adolescence.
Early detection and management are critical for minimizing these risks.
Treatment Options for Delayed or Failed Descent
If tests do not descend naturally within six months after birth, medical intervention might be necessary. This condition—cryptorchidism—affects approximately 1-4% of full-term male infants by one year old.
Treatment approaches include:
Hormonal Therapy
Human chorionic gonadotropin (hCG) injections have been used historically to stimulate testosterone production aiming to encourage testicular descent. However, success rates vary widely (20-30%), making hormonal therapy less favored today except in select cases.
Surgical Intervention (Orchiopexy)
Surgery remains the gold standard treatment for undescended testes beyond infancy. Orchiopexy involves mobilizing and fixing each testis securely within the scrotum under general anesthesia.
Timing matters here; surgery ideally occurs before 12-18 months old to optimize fertility outcomes and reduce cancer risk later on. Delays beyond this window correlate with poorer prognoses.
The Variability: What if Descent Happens Late?
In some cases, testicles may descend late—sometimes even after birth but before six months old—in what’s called “ascending” or “retractile” testes due to active cremasteric muscle contractions pulling them upward intermittently.
These cases often resolve without intervention but require monitoring because persistent undescended status beyond six months usually warrants treatment consideration.
Regular pediatric checkups include genital exams precisely for such reasons—to track proper positioning over time rather than jumping prematurely into surgery unless necessary.
Anatomical Differences: Unilateral vs Bilateral Undescended Testes
Cryptorchidism can affect one side (unilateral) or both sides (bilateral). Unilateral cases are more common (~75%), while bilateral occurs less frequently (~25%).
| Unilateral Cryptorchidism | Bilateral Cryptorchidism | |
|---|---|---|
| Affected Side(s) | One testis fails to descend. | Both testes fail to descend. |
| Surgical Complexity | Surgery usually straightforward on one side. | Surgery more extensive; fertility impact greater risk. |
| Poor Fertility Risk? | Slightly reduced if other testis normal. | Larger fertility concerns due to both affected. |
Understanding which type helps tailor treatment plans accordingly while informing parents about potential outcomes clearly.
The Connection Between Prematurity & Testicular Descent Timing
Premature infants face higher rates of cryptorchidism compared to full-term babies due mainly to incomplete gestational development at birth. Since much of testicular descent occurs late in pregnancy (after week 28), preemies often have undescended testes at birth simply because they haven’t had enough time for natural migration yet.
Fortunately, many premature infants experience spontaneous descent within several months postnatally once they reach corrected gestational age milestones near term equivalence (~40 weeks).
Pediatricians closely monitor these infants’ genital status before deciding on intervention timing so unnecessary procedures aren’t performed prematurely on potentially descending gonads.
Key Takeaways: When Do Testes Descend Into Scrotum?
➤ Testes begin descent around the 7th month of fetal development.
➤ Descent completes before birth in most full-term infants.
➤ Hormones like testosterone regulate the descent process.
➤ Failure to descend is known as cryptorchidism.
➤ Early diagnosis is crucial for proper treatment and fertility.
Frequently Asked Questions
When do testes descend into scrotum during fetal development?
The testes typically descend into the scrotum between 28 and 35 weeks of gestation. This crucial process ensures the testes move from the abdomen through the inguinal canal to their final position in the scrotal sac, which is essential for proper male reproductive function.
When do testes begin their descent into the scrotum?
The descent begins early in fetal development with the transabdominal phase occurring between weeks 8 and 15. During this time, the testes move from near the kidneys down to the internal inguinal ring, guided by hormonal and mechanical factors.
When do testes complete their descent into the scrotum?
The testes usually complete their descent into the scrotum between weeks 28 and 35 of gestation. This final phase, known as the inguinoscrotal phase, involves testosterone-driven migration through the inguinal canal to reach the scrotal sac.
When do hormonal changes influence testes descent into the scrotum?
Hormonal changes influence testicular descent throughout gestation. INSL3 plays a key role during weeks 8 to 15, while testosterone is critical from about week 25 until birth to stimulate movement through the inguinal canal into the scrotum.
When do complications arise if testes fail to descend into scrotum?
If testes fail to descend by birth, a condition called cryptorchidism occurs. This can lead to fertility issues or increased cancer risk later in life. Early diagnosis and treatment are important to address this problem effectively.
The Bottom Line – When Do Testes Descend Into Scrotum?
The journey of testicles from abdomen into scrotum is a finely tuned developmental event occurring mostly between weeks 28 and 35 of gestation under hormonal control involving INSL3 and testosterone. Proper anatomical structures guide this migration through two distinct phases ensuring optimal positioning at birth for future reproductive health.
While natural variation exists—with some late descents happening shortly after delivery—the majority complete this process prenatally or very soon after birth. Failure leads to cryptorchidism requiring timely diagnosis and often surgical correction before age two years for best outcomes regarding fertility preservation and cancer prevention.
Monitoring boys’ genital development closely right after birth remains essential so any deviations from normal timing don’t go unnoticed or untreated unnecessarily long. With current medical understanding combined with advances in neonatal care, most boys with delayed or failed testicular descent achieve healthy results following appropriate management strategies tailored individually based on timing, anatomy, and associated risk factors.