
If she has re absorbed twice at 6 week I would be thinking luteal failure, I would recommend you seek advice from repor specialist before you mate again and monitor progesterone throughout pregnancy. If they are falling hormonal support can be given to maintain pregnancy BUT this will need to be carefully managed by repro vet rather than GP vet.
Extract from :
http://www.labbies.com/reproduction2.htmProgesterone Insufficiency. Bitches for which pregnancy has been confirmed by ultrasound or serum relaxin diagnosis (refer to "Pregnancy Diagnosis" in Part 1) and subsequently experience spontaneous abortion without evidence of any of the infectious causes outlined above should be suspected of having progesterone insufficiency (insufficient luteal phase). Progesterone hormone rises just prior to ovulation and continues to increase to levels above 5 ng/ml during the pregnancy then will decrease just prior to whelping. This hormone is essential for the maintenance of the pregnancy because it is required in high levels to suppress the hypothalamus from producing gonadotropin releasing hormone (GnRH). If levels of progesterone drop below 2 ng/ml, GnRH levels will rise and stimulate the pituitary to release follicular stimulating hormone (FSH) and lutenizing hormone (LH). FSH and LH will reset the ovarian cycle causing an abrupt termination of the current cycle, thus resulting in spontaneous abortion. This premature decrease in progesterone will typically occur between 2 and 4 weeks after breeding. When the condition occurs early in gestation, prior to confirmation of pregnancy, diagnosis is often complicated because other factors associated with unsuccessful breeding must be ruled out. Bitches for which there is a strong suspicion of progesterone insufficiency or that are confirmed to be pregnant prior to spontaneous abortion with no evidence of other conditions should be monitored for serum progesterone levels by ELISA during subsequent pregnancies. In such an instance, progesterone levels are measured from the time of breeding through the weeks of gestation. If progesterone levels begin to fall, exogenous progesterone therapy can be administered to maintain the pregnancy. Progesterone therapy is discontinued at the end of the gestation period with birth occurring within 72 hours after the final injection is administered.