The gender of the chicken to take for Kaparos:[1]

One is to take a male chicken for a male family member, and a female chicken for a female family member.

Pregnant woman:[2] For a pregnant woman one is to take and slaughter one female chicken on her behalf, and one female and male chicken on behalf of the fetus whose gender is in question. [Thus, in total, a pregnant woman takes three chickens, two females and one male.]

What is the law if a woman used a male chicken or vice versa?[3]

She fulfills her obligation. The Kaparos is not required to be repeated.

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[1] Admur 605:3; Siddur Admur; Rama 605:1

[2] Siddur Admur; Second custom in Admur 605:3; Poskim ibid in previous footnotes

Ruling of Admur in Shulchan Aruch 605:3: In the Shulchan Aruch 605:3 Admur records a difference in custom and rules as follows: According to the first custom [brought in previous footnotes] that allows exempting many males with one chicken and many females with one chicken, one is only required to take for a pregnant woman two chickens, one male and one female chicken. [Admur ibid; Rama 605:1; M”A 605:2; Mahril] The reason for this is because if the fetus is a male, then he has one male chicken as required, and if it is a female, then it suffices for the mother and fetus to have one female chicken. [Admur ibid; M”A ibid] However according to the second custom mentioned to take a chicken for each family member, a male for a boy, female for a girl, then one is to take for a pregnant woman three chickens, two females and one male. [Admur ibid] 

[3] Ashel Avraham Butschetch Tinyana 605