How to determine pregnancy in a rat? - briefly
Pregnancy is identified by abdominal palpation of embryonic vesicles around days 12–14 post‑mating, by measuring elevated plasma progesterone, or by ultrasound imaging after day 15; definitive confirmation is obtained through necropsy.
How to determine pregnancy in a rat? - in detail
Detecting gestation in laboratory rats requires a combination of physical observation, biochemical testing, and imaging techniques.
Physical signs appear within 7–10 days after mating. The abdomen enlarges gradually; a 5–10 % increase in body weight is typical by day 14. Palpation of the abdomen may reveal uterine swellings, although the procedure can cause stress and should be performed gently. The presence of a copulatory plug in the vaginal opening, observable shortly after mating, confirms that copulation occurred but does not guarantee conception.
Vaginal cytology provides a reliable early indicator. A smear collected with a sterile swab and examined under a microscope shows a shift from predominantly leukocytes to cornified epithelial cells. This luteal phase pattern emerges 3–4 days post‑coitus and persists throughout pregnancy.
Hormonal assays quantify serum concentrations of progesterone and estradiol. Progesterone levels rise sharply after implantation and remain elevated until parturition. Commercial ELISA kits can detect concentrations as low as 0.5 ng/mL, allowing confirmation of pregnancy by day 8–10.
Ultrasound imaging offers non‑invasive visualization of embryonic structures. A high‑frequency transducer (≥30 MHz) applied to the shaved abdominal area detects fetal heartbeats and placental development from day 12 onward. Ultrasound provides precise dating of gestational age and monitors fetal viability.
Necropsy remains the definitive method for confirming pregnancy in research settings where terminal procedures are permitted. Dissection of the uterine horns reveals implantation sites, each appearing as a distinct swelling containing an embryo surrounded by decidual tissue.
Practical workflow for confirming gestation
- Observe for copulatory plug within 24 h of pairing.
- Record daily body weight; note a consistent increase exceeding 5 % by day 14.
- Collect vaginal smears on days 3–5; identify predominance of cornified cells.
- Draw blood on days 8–10; measure progesterone via ELISA.
- Perform abdominal ultrasound on day 12 or later; confirm fetal heart activity.
- If required, conduct necropsy to enumerate implantation sites.
Combining these approaches yields a robust assessment of pregnancy status, minimizes false‑positive results, and supports accurate scheduling of experimental procedures.