In a paternity proceeding, the appeal is from an order of filiation of the Family Court, Richmond County (Meyer, J.), dated October 23, 1979. On the court’s own motion, leave to appeal from the order of filiation is granted (see Family Ct Act, § 1112). Order of filiation reversed, on the law and the facts, without costs or disbursements, order of support dated January 30,1980 vacated, and the matter is remitted to the Family Court, Richmond County, for further proceedings in accordance herewith. Petitioner’s testimony indicated that the earliest possible act of sexual intercourse from which conception could have occurred was on July 9, 1978. The child was born on March 17, 1979. The period of gestation was thus at most 251 days from conception. The normal period of gestation is 266 days from the date of conception. Where there is a substantial deviation from this norm, expert medical testimony is necessary prior to a finding of paternity (Matter of Karen K. v Christopher D., 86 AD2d 633; Matter of Erie County Comr. of Social Servs. v Boyd, 74 AD2d 728; see, also, Matter of Department of Social Servs. v Charles L., 78 AD2d 875). A period of 251 days is a substantial deviation (see Matter of Karen K. v Christopher D., supra [256 days from conception]). Accordingly, the matter is remitted to Family Court for a new hearing, at which expert medical testimony should be adduced. We would also direct the parties’ attention to the newly adopted sections 418 and 532 of the Family Court Act, which permit the use of the human leucocyte antigen blood tissue test. The test is highly accurate on the issue of paternity and should be utilized to avoid unnecessary litigation. Weinstein, J. P., O’Connor, Bracken and Rubin, JJ., concur.