Known Maternal Carrier — Offspring Risk Calculator BETA TESTING

Estimates the approximate risk that a pregnancy will result in an affected child for selected disorders, assuming the mother is a known carrier and the father is clinically unaffected and untested. Autosomal recessive conditions use paternal carrier risk based on ancestry; X-linked conditions use Mendelian inheritance and do not depend on paternal ancestry.

Key assumptions

Mother is a known heterozygous carrier for: cystic fibrosis (CF), spinal muscular atrophy (SMA), α-thalassemia, sickle cell disease, HBB-related hemoglobinopathies (β-thalassemia and related), Tay-Sachs disease, phenylketonuria (PKU), lysosomal storage disorders (combined autosomal recessive panel), hereditary hemochromatosis, congenital adrenal hyperplasia (21-hydroxylase–deficient CAH), autosomal recessive polycystic kidney disease (ARPKD), Fanconi anemia, hemophilia A, hemophilia B, Duchenne/Becker muscular dystrophy, and Fragile X syndrome.
Father is clinically unaffected, has no known family history, and has not had carrier testing for these conditions.
Autosomal recessive: Risk of affected child ≈ paternal carrier probability × 25% (1 in 4) when both parents are carriers.
X-linked (hemophilia A/B, DMD/BMD): simplified model assumes approximately 1 in 4 pregnancies (25%) result in an affected child if the mother is a carrier and fetal sex is unknown, and ~50% risk of an affected male when a male fetus is known.
Fragile X (FMR1-related) is more complex: risk of an affected child depends on whether the mother has a premutation or full mutation, the CGG repeat size and probability of expansion to a full mutation, fetal sex, and X-inactivation in females; this tool presents an approximate risk only and should be interpreted together with formal genetic counseling.

Select the father’s primary ancestry

Father’s primary ancestry / ethnicity

After calculating, use the checkboxes in each panel to toggle which conditions are included in the printed counseling summary.

Panel — Autosomal recessive: CF, SMA, α-thalassemia

Conditions

Cystic fibrosis (CFTR)
Spinal muscular atrophy (SMA, SMN1-related)
α-Thalassemia (clinically significant syndromes)

Panel — Autosomal recessive: hemoglobinopathies, metabolic and multisystem disorders

Conditions

Sickle cell disease (HbSS and related sickling disorders)
HBB-related hemoglobinopathies / β-thalassemia
Tay-Sachs disease
Phenylketonuria (PKU)
Lysosomal storage disorders (combined AR panel)
Hereditary hemochromatosis (HFE-associated)
Congenital adrenal hyperplasia (21-hydroxylase–deficient CAH)
Autosomal recessive polycystic kidney disease (ARPKD, PKHD1-related)
Fanconi anemia (AR forms)

Panel — X-linked: bleeding and neuromuscular / neurodevelopmental disorders

Conditions

Hemophilia A (factor VIII deficiency)
Hemophilia B (factor IX deficiency)
Duchenne / Becker muscular dystrophy (DMD gene)
Fragile X syndrome (FMR1-related)

Counseling Summary — Known Maternal Carrier

Condition	Inheritance	Risk of affected child per pregnancy	Counseling notes

References — carrier frequencies, inheritance, and epidemiology

American College of Obstetricians and Gynecologists. Committee Opinion No. 691: Carrier screening for genetic conditions. Obstet Gynecol. 2017;129(3):e41–e55. Available at: https://www.acog.org/clinical/clinical-guidance/committee-opinion/articles/2017/03/carrier-screening-for-genetic-conditions .
Goldberg JD, Kalia SS, et al. Expanded carrier screening: what conditions should we screen for? Prenat Diagn. 2023;43(5):575–584. Available at: https://obgyn.onlinelibrary.wiley.com/doi/full/10.1002/pd.6306 .
Pletcher BA, Bejjani BA, et al. Cystic Fibrosis. In: Adam MP, Bick S, Mirzaa GM, et al., eds. GeneReviews [Internet]. Seattle (WA): University of Washington, Seattle; 1993–. Available at: https://www.ncbi.nlm.nih.gov/books/NBK1250/ .
MedlinePlus Genetics. Cystic fibrosis. Available at: https://medlineplus.gov/genetics/condition/cystic-fibrosis/ .
Prior TW, Finanger E. Spinal Muscular Atrophy. In: Adam MP, Bick S, Mirzaa GM, et al., eds. GeneReviews [Internet]. Seattle (WA): University of Washington, Seattle; updated 2020. Available at: https://www.ncbi.nlm.nih.gov/books/NBK1352/ .
MedlinePlus Genetics. Spinal muscular atrophy. Available at: https://medlineplus.gov/genetics/condition/spinal-muscular-atrophy/ .
Tamary H, Dgany O. Alpha-Thalassemia. In: Adam MP, Bick S, Mirzaa GM, et al., eds. GeneReviews [Internet]. Seattle (WA): University of Washington, Seattle; updated 2024. Available at: https://www.ncbi.nlm.nih.gov/books/NBK1435/ .
MedlinePlus Genetics. Alpha thalassemia. Available at: https://medlineplus.gov/genetics/condition/alpha-thalassemia/ .
Bender MA. Sickle Cell Disease. In: Adam MP, Bick S, Mirzaa GM, et al., eds. GeneReviews [Internet]. Seattle (WA): University of Washington, Seattle; updated 2025. Available at: https://www.ncbi.nlm.nih.gov/books/NBK1377/ .
National Organization for Rare Disorders (NORD). Sickle cell disease. Available at: https://rarediseases.org/rare-diseases/sickle-cell-disease/ .
Langer AL. Beta-Thalassemia. In: Adam MP, Bick S, Mirzaa GM, et al., eds. GeneReviews [Internet]. Seattle (WA): University of Washington, Seattle; updated 2024. Available at: https://www.ncbi.nlm.nih.gov/books/NBK1426/ .
MedlinePlus Genetics. Beta thalassemia. Available at: https://medlineplus.gov/genetics/condition/beta-thalassemia/ .
Toro C, et al. HEXA Disorders (including Tay-Sachs disease). In: Adam MP, Bick S, Mirzaa GM, et al., eds. GeneReviews [Internet]. Seattle (WA): University of Washington, Seattle; updated 2020. Available at: https://www.ncbi.nlm.nih.gov/books/NBK1218/ .
MedlinePlus Genetics. Tay-Sachs disease. Available at: https://medlineplus.gov/genetics/condition/tay-sachs-disease/ .
Regier DS, Greene CL, et al. Phenylalanine Hydroxylase Deficiency. In: Adam MP, Bick S, Mirzaa GM, et al., eds. GeneReviews [Internet]. Seattle (WA): University of Washington, Seattle; 2017. Available at: https://www.ncbi.nlm.nih.gov/books/NBK1504/ .
MedlinePlus Genetics. PAH gene. Available at: https://medlineplus.gov/genetics/gene/pah/ .
American College of Obstetricians and Gynecologists. Management of Women with Phenylalanine Hydroxylase Deficiency (Phenylketonuria). Committee Opinion No. 802. 2020. Available at: https://www.acog.org/clinical/clinical-guidance/committee-opinion/articles/2020/04/management-of-women-with-phenylalanine-hydroxylase-deficiency-phenylketonuria .
La Cognata V, et al. Highlights on genomics applications for lysosomal storage diseases. Genes (Basel). 2020;11(8):777. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7465195/ .
Chang S, et al. Newborn Screening for 6 Lysosomal Storage Disorders in Shanghai, China. JAMA Netw Open. 2024;7(6):e2412345 (example). Available at: https://jamanetwork.com/journals/jamanetworkopen/fullarticle/2818643 .
Barton JC, Edwards CQ, Acton RT. HFE-Related Hemochromatosis. In: Adam MP, Bick S, Mirzaa GM, et al., eds. GeneReviews [Internet]. Seattle (WA): University of Washington, Seattle; updated 2024. Available at: https://www.ncbi.nlm.nih.gov/books/NBK1440/ .
MedlinePlus Genetics. HFE-associated hereditary hemochromatosis. Available at: https://medlineplus.gov/genetics/condition/hereditary-hemochromatosis/ .
Nimkarn S, Gangishetti PK, et al. 21-Hydroxylase-Deficient Congenital Adrenal Hyperplasia. In: Adam MP, Bick S, Mirzaa GM, et al., eds. GeneReviews [Internet]. Seattle (WA): University of Washington, Seattle; updated 2016. Available at: https://www.ncbi.nlm.nih.gov/books/NBK1171/ .
MedlinePlus Genetics. 21-hydroxylase deficiency. Available at: https://medlineplus.gov/genetics/condition/21-hydroxylase-deficiency/ .
Burgmaier K, Gimpel C, Schaefer F, et al. Autosomal Recessive Polycystic Kidney Disease – PKHD1. In: Adam MP, Bick S, Mirzaa GM, et al., eds. GeneReviews [Internet]. Seattle (WA): University of Washington, Seattle; updated 2024. Available at: https://www.ncbi.nlm.nih.gov/books/NBK1326/ .
National Organization for Rare Disorders (NORD). Autosomal recessive polycystic kidney disease. Available at: https://rarediseases.org/rare-diseases/autosomal-recessive-polycystic-kidney-disease/ .
Mehta PA, Ebens C. Fanconi Anemia. In: Adam MP, Bick S, Mirzaa GM, et al., eds. GeneReviews [Internet]. Seattle (WA): University of Washington, Seattle; updated 2021. Available at: https://www.ncbi.nlm.nih.gov/books/NBK1401/ .
MedlinePlus Genetics. Fanconi anemia. Available at: https://medlineplus.gov/genetics/condition/fanconi-anemia/ .
Konkle BA, Huston H, Nakaya Fletcher S. Hemophilia A. In: Adam MP, Bick S, Mirzaa GM, et al., eds. GeneReviews [Internet]. Seattle (WA): University of Washington, Seattle; updated 2023. Available at: https://www.ncbi.nlm.nih.gov/books/NBK1404/ .
Konkle BA, Nakaya Fletcher S. Hemophilia B. In: Adam MP, Bick S, Mirzaa GM, et al., eds. GeneReviews [Internet]. Seattle (WA): University of Washington, Seattle; updated 2024–2025. Available at: https://www.ncbi.nlm.nih.gov/books/NBK1495/ .
MedlinePlus Genetics. Hemophilia. Available at: https://medlineplus.gov/genetics/condition/hemophilia/ .
Darras BT, Urion DK, Ghosh PS. Dystrophinopathies. In: Adam MP, Bick S, Mirzaa GM, et al., eds. GeneReviews [Internet]. Seattle (WA): University of Washington, Seattle; updated 2022. Available at: https://www.ncbi.nlm.nih.gov/books/NBK1119/ .
MedlinePlus Genetics. Duchenne and Becker muscular dystrophy. Available at: https://medlineplus.gov/genetics/condition/duchenne-and-becker-muscular-dystrophy/ .
Hunter JE, Berry-Kravis E, Hipp HS, et al. FMR1 Disorders. In: Adam MP, Bick S, Mirzaa GM, et al., eds. GeneReviews [Internet]. Seattle (WA): University of Washington, Seattle; updated 2024. Available at: https://www.ncbi.nlm.nih.gov/books/NBK1384/ .
MedlinePlus Genetics. Fragile X syndrome. Available at: https://medlineplus.gov/genetics/condition/fragile-x-syndrome/ .

Disclaimer
All calculations must be confirmed before clinical use. These estimates are based on population-level carrier frequencies and simple Mendelian models, and do not account for admixture, founder mutations, variable penetrance (for example in HFE-related hemochromatosis), or specific parental genotypes (e.g., α-thalassemia deletion patterns, HBB genotype, FMR1 CGG repeat size). This tool is intended as an aid to genetic counselors . It does not replace consultation with a genetics professional, laboratory-specific residual risk tables, or formal preconception/prenatal counseling. Neither Perinatology.com nor any individual, organization, or other party involved in the preparation or publication of this website shall be liable for any special, consequential, or exemplary damages resulting in whole or part from any use of or reliance upon the results or values generated by this calculator.