At 4 months pregnant, a false negative result could be due to a damaged/non-functioning test or possibly a performance error. The concentration of the hormone hCG in the 4th month of pregnancy is very high, so even taking a test of diluted urine (not morning), would give a positive result.

And even in the 4th month hcg would be low not to detect?

Yes, it is possible to get a negative urine pregnancy test result while pregnant. This result is called a false negative. Urine pregnancy tests are based on the identification in the urine of the pregnancy hormone - chorionic gonadotropin (beta hCG), the concentration of which increases as pregnancy develops. Obtaining a false negative pregnancy test result can be influenced by, m.in. too early performance of the test - when the beta hCG level is too low, too much dilution of urine by taking a large amount of fluids, too fast reading of the obtained result or the test was expired. Each test comes with an instruction manual and the time you need to wait to be able to read the test result. Some tests require you to wait up to 10 minutes, so please follow the instructions and recommendations of the test manufacturer when performing it. In the following link, you can compare prices and book the selected test at the pharmacy or order with home delivery: https://www.gdziepolek.pl/kategorie/test-ciazowy In addition, I enclose materials that may be helpful: https://www.gdziepolek.pl/artykuly/test-ciazowy-jaki-wybrac-i-kiedy-zrobic#czy-negatywny-test-ciazowy-zawsze-oznacza-brak-ciazy