The use of laser and optoelectronics concepts to develop biological detection systems is the goal of this work. A biosensor based on one of the interferometer techniques, Mach-Zhender interferometer (MZI) technique, and the using of the laser beam is developed for pregnancy detection or pregnancy hormone, Human chorionic gonadotropin (HCG), increasing. A part of photonic crystal fiber (PCF) with 3 different lengths (1.5 cm, 1.0 cm, and 0.5 cm) has been collapsed with 2 conventional single mode fibers (SMFs) to achieve MZI technique, Micro-holes collapsing and make high sensitive regions for the optical properties (refractive index and absorption) in the urine sample. This type of laser biosensor depends on light intensity measurement through a modified optical fiber. The sensing region is immersed in different urine samples of pregnant female and non-pregnant female. Biological changes in the urine sample due to the HCG increasing lead to a change in the optical properties (refractive index and absorption) of the urine sample. The results showed that the increasing of pregnancy hormones leads to an increase in the refractive index for a urine sample and a decrease in the intensity of the output laser beam. From this test, the calibration curve of laser biosensor for a pregnancy test or pregnancy detection has been found. The sensitivities of the laser biosensor with a refractive index in the range (1.33864-1.34257) at (1.5 cm, 1.0 cm, and 0.5 cm) PCF length are 61.142 ABS/ RIU, 4.5132 ABS/RIU and 2.888 ABS/RIU, respectively. Thus, the highest sensitivity was found for the (1.5 cm) photonic crystal fiber length.