; and (3) by inserting after subparagraph (C) the following new subparagraph: (D) that, as of January 1, 2000, was maintained by an employer— (i) described in section 501(c)(3), (ii) who has been in existence since at least 1938, (iii) who conducts medical research directly or indirectly through grant making, and (iv) whose primary exempt purpose is to provide services with respect to mothers and children. . (c) Effective date The amendments made by this section shall apply to plan years beginning after December 31, 2018. 406. Extended amortization for single employer plans (a) 15-Year amortization under the Internal Revenue Code of 1986 Section 430(c) of the Internal Revenue Code of 1986 is amended by adding at the end the following new paragraph: (8) 15-year amortization With respect to plan years beginning after December 31, 2019— (A) the shortfall amortization bases for all plan years preceding the first plan year beginning after December 31, 2019 (and all shortfall amortization installments determined with respect to such bases) shall be reduced to zero, and (B) subparagraphs (A) and (B) of paragraph (2) shall each be applied by substituting 15-plan-year period for 7-plan-year period . . (b) 15-Year amortization under the Employee Retirement Income Security Act of 1974 Section 303(c) of the Employee Retirement Income Security Act of 1974 ( 29 U.S.C. 1083(c) ) is amended by adding at the end the following new paragraph: (8) 15-year amortization With respect to plan years beginning after December 31, 2019— (A) the shortfall amortization bases for all plan years preceding the first plan year beginning after December 31, 2019 (and all shortfall amortization installments determined with respect to such bases) shall be reduced to zero, and (B) subparagraphs (A) and (B) of paragraph (2) shall each be applied by substituting 15-plan-year period for 7-plan-year period . . (c) Effective date The amendments made by this section shall apply to plan years beginning after December 31, 2019. 407. Extension of pension